METHOD AND DEVICE FOR CHARACTERIZING THIN LAYERS

Abstract

One method involves generating a source beam of heterodyne light directed at a test layer such that the source beam strikes the test layer at a first angle of incidence. The source beam is polarized, creating a reference beam. A portion of the source beam reflected by the test layer is also polarized, creating a test beam. Intensity signals of the reference beam and test beam are measured. A phase difference between the intensity signals of the test beam and the reference beam is determined. Based on this phase difference, the refractive index, extinction coefficient, and thickness of the test layer are calculated.

Description

background

[0001] Numerous modern tools used to characterize semiconductor device layers and / or layers used in semiconductor device fabrication utilize optical devices for non-contact measurement. One such optical device is a reflectometer, which measures the reflectance resulting from incident optical radiation interacting with a test layer. Another such optical device is an interferometer, which measures interference resulting from incident optical radiation interacting with a test layer. A further such optical device is an ellipsometer, which measures elliptical polarization resulting from incident optical radiation interacting with a test layer. Brief description of the drawings

[0002] Aspects of this disclosure are best understood with reference to the following detailed description in conjunction with the accompanying drawings. It should be noted that, in accordance with industry practice, various elements are not shown to scale. Rather, the dimensions of the various elements may have been arbitrarily enlarged or reduced for the sake of clarity. Fig. Figure 1 shows a block diagram of some embodiments of a device for measuring the thickness, refractive index and extinction coefficient of a sample. Fig. Figure 2 shows a diagram of some embodiments of a test intensity signal and a reference intensity signal. Fig. Figure 3 shows a block diagram of some further embodiments of the device of Fig. 1. Fig. Figure 4 shows a diagram of some embodiments of a first test intensity signal, a second test intensity signal and a reference intensity signal. Fig. Figure 5 shows a diagram of some embodiments of distributions of a thickness, a refractive index and an extinction coefficient for a layer of the sample. Fig. Figure 6 shows a block diagram of some further embodiments of the device of Fig. 3. The Fig. 7, Fig. 8 and Fig. Figure 9 shows diagrams of some further embodiments of the device of Fig. 6. The Fig. 10, Fig. 11, Fig. 12 to Fig. Figure 13 shows sectional views of some embodiments of the sample. Fig. Figure 14 shows a diagram of some embodiments of distributions of a thickness, a refractive index and an extinction coefficient for a plurality of layers of the sample. The Fig. 15, Fig. 16 to Fig. Figure 17 shows block diagrams of some embodiments of a method for determining a refractive index, an extinction coefficient and a thickness of a sample. The Fig. 18, Fig. 19 to Fig. Figure 20 shows block diagrams of some further embodiments of a method for determining a refractive index, an extinction coefficient and a thickness of a sample. The Fig. 21, Fig. 22 to Fig. Figure 23 shows block diagrams of some further embodiments of a method for determining a refractive index, an extinction coefficient and a thickness of a sample. Fig. Figure 24 shows a flowchart of some embodiments of a method for determining distributions of the refractive index, the extinction coefficient and the thickness of the layer(s) of a sample across a surface of the sample. Detailed description

[0003] The disclosure below provides many different embodiments or examples for implementing various features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the fabrication of a first element over or on top of a second element in the description below may include embodiments in which the first and second elements are fabricated in direct contact, and it may also include embodiments in which additional elements can be fabricated between the first and second elements, such that the first and second elements are not in direct contact. Furthermore, reference numerals and / or letters may be repeated in the various examples in the present disclosure.This repetition serves the purpose of simplicity and clarity and does not in itself prescribe any relationship between the various designs and / or configurations discussed.

[0004] Furthermore, spatially relative terms, such as "located below," "under," "lower," "located above," "upper," and the like, can be used here to simply describe the relationship of one element or structural element to one or more other elements or structural elements depicted in the figures. These spatially relative terms are intended to encompass orientations of the device in use or operation beyond the orientation shown in the figures. The device may be oriented differently (rotated by 90° or in a different orientation), and the spatially relative descriptors used here can be interpreted accordingly.

[0005] The fabrication of semiconductor devices often involves the fabrication and / or use of thin films (e.g., thin films). Some thin films (e.g., dielectric thin films, conductive thin films, semiconductor thin films, etc.) are placed on or over a substrate, while others are self-contained (e.g., pellicles for photolithography). Characterizing these thin films can be an important part of semiconductor device fabrication. For example, determining the thickness, refractive index, extinction coefficient, and / or other properties of these thin films can be important for performance evaluation, quality control, or similar purposes.

[0006] In some examples, the thickness, refractive index, and extinction coefficient of a test layer can be determined using a spectroscopic ellipsometric process. Stoichiometric ellipsometry involves modeling (e.g., evaluating) the structure of a test layer. A light source generates a linearly polarized beam of light directed to a point along the test layer. This beam strikes the test layer at that point, and the layer reflects an elliptically polarized beam. A change in polarization is determined by polarizing the reflected beam with an analyzer and measuring the intensity of the polarized reflected beam with a light sensor. The thickness, refractive index, and extinction coefficient of the test layer are then determined based on the measured change in polarization and the model of the test layer.

[0007] One challenge of the spectroscopic ellipsometry process is that an exact model is required to precisely determine the thickness, refractive index, and extinction coefficient of the test layer based on the measured change in polarization. Accurately modeling the test layer can be difficult, thus increasing the likelihood of inaccurate results. Another challenge is that environmental factors (e.g., vibration, atmospheric disturbances) can affect the polarization of the beam between the light source and the test layer, and between the test layer and the light sensor. This can influence the change in polarization measured by the light sensor, potentially reducing the robustness of the spectroscopic ellipsometry process.

[0008] In various embodiments of the present disclosure, the thickness, refractive index, and extinction coefficient of the test layer are determined using a heterodyne reflectometry and common-path interferometry process to improve accuracy and robustness. The process involves generating a source beam of heterodyne light using a heterodyne light source. A first portion of the source beam is polarized by a first analyzer, creating a reference beam. Polarization by the first analyzer causes the source beam to interfere with itself, resulting in self-interference of the reference beam. The self-interference of the reference beam is measured by measuring an intensity signal of the reference beam with a first light sensor. A second portion of the source beam is then directed onto the test layer.A portion of the incident beam is reflected by the test layer and then polarized by a second analyzer, creating a test beam. Polarization by the second analyzer causes the reflected beam to interfere with itself (e.g., through common-path interference), resulting in self-interference within the test beam. This self-interference is measured by measuring the intensity signal of the test beam with a second light sensor. A phase difference is determined between the intensity signal of the test beam and the intensity signal of the reference beam. The thickness, refractive index, and extinction coefficient of the test layer are then calculated based on this phase difference.

[0009] This heterodyne reflectometry / interferometry process does not rely on an exact model of the test layer to precisely measure its thickness, refractive index, and extinction coefficient. Therefore, the measurement accuracy can be improved. Furthermore, because this process utilizes heterodyne common-path interferometry, environmental factors have less influence on the measured intensity of the reference and test beams. This enhances the robustness of the measurement.

[0010] Fig. Figure 1 shows a block diagram of some embodiments of a device for measuring the thickness, refractive index and extinction coefficient of a sample 108.

[0011] The device includes a heterodyne light source 102, a beam splitter 104, a first analyzer 110, a second analyzer 112, a first light sensor 114, a second light sensor 116 and a characterization circuit 118.

[0012] The beam splitter 104 is arranged between the heterodyne light source 102 and a sample 108. The first analyzer 110 is arranged directly between the beam splitter 104 and the first light sensor 114. The second analyzer 112 is arranged directly between the sample 108 and the second light sensor 116. The characterization circuit 118 is connected to the first light sensor 114 and the second light sensor 116. For example, a first input of the characterization circuit 118 is connected to an output of the first light sensor 114, and a second input of the characterization circuit 118 is connected to an output of the second light sensor 116.

[0013] Sample 108 has a test layer (e.g., a layer 1002 of the Fig. 10, Fig. 11, Fig. 12 to Fig. 13) on. In some embodiments, the test layer is independent (as is the case, for example, in Fig. 10). In some other embodiments, the test layer is arranged on a substrate (as is shown, for example, in Fig. 11). In some embodiments, the sample 108 has a plurality of independent test layers stacked on top of each other (as is shown, for example, in Fig. 12). In some further embodiments, the sample 108 has a plurality of test layers stacked on top of each other on a substrate (as is shown, for example, in Fig. 13 is shown).

[0014] The heterodyne light source 102 generates a source beam 130 of heterodyne light directed towards the sample 108. The source beam 130 contains s-polarized light (e.g., light with an electric field polarized perpendicular to the plane of incidence) and p-polarized light (e.g., light with an electric field polarized parallel to the plane of incidence). A phase difference between the phase of the s-polarized light and the phase of the p-polarized light of the source beam 130 is modulated.

[0015] The beam splitter 104 reflects a first part of the source beam 130, creating a splitter-reflected beam 134. The first analyzer 110 polarizes the splitter-reflected beam 134, causing the s-polarized and p-polarized light of the splitter-reflected beam 134 to interfere with each other (e.g., by common-path interference), creating a reference beam 140 (e.g., the beam resulting from the interference). The first light sensor 114 measures the intensity of the reference beam 140 over a period of time, which is represented by a reference beam intensity signal I. ref from Fig. 2 is shown.

[0016] The beam splitter 104 allows a second part of the source beam 130 to pass through, creating an incident beam 132. The sample 108 reflects a part of the incident beam 132, creating a sample-reflected beam 136. This interaction (e.g., reflection) with the sample 108 can influence the phase difference between the s- and p-polarized light. For example, this interaction can cause the phase difference between the s- and p-polarized light of the sample-reflected beam 136 to differ from the phase difference between the s- and p-polarized light of the incident beam 132. The second analyzer 112 polarizes the sample-reflected beam 136, causing the s- and p-polarized light of the sample-reflected beam 136 to interfere with each other (e.g.,through common-path interference), resulting in a test beam 138 (e.g., the beam resulting from the interference). The second light sensor 116 measures an intensity of the test beam 138 during the period, which is indicated by a test beam intensity signal I. test in Fig. 2 is shown.

[0017] The characterization circuit 118 determines a phase φ ref of the reference beam intensity signal I ref , which indicates the phase difference between the s- and p-polarized light of the reference beam 140. The characterization circuit 118 determines a phase φ test of the test beam intensity signal I test , which indicates the phase difference between the s- and p-polarized light of the test beam 138.

[0018] Furthermore, the characterization circuit 118 determines a phase difference φ diff between the phase φ testof the test beam intensity signal I test and the phase φ ref of the reference beam intensity signal I ref By subtracting the phase φ ref of the reference beam intensity signal I ref from phase φ test of the test beam intensity signal I test The portion of the phase difference between the s- and p-polarized light of the test beam 138 that is caused by the interaction with the sample 108 can be determined. The influence of the sample 108 on the phase difference between the s- and p-polarized light of the test beam 138 is used to determine several properties of the sample 108. For example, the characterization circuit 118 determines the thickness, refractive index, and extinction coefficient of the layer(s) of the sample 108 based on the phase difference φ. diff .

[0019] Since this heterodyne reflectometry, using the heterodyne common-path interferometry process, does not rely on an exact model of sample 108 to precisely measure its thickness, refractive index, and extinction coefficient, the measurement accuracy can be improved. Furthermore, because this process utilizes heterodyne common-path interferometry, environmental factors (e.g., vibration, air disturbances, etc.) have a lesser influence on the results. This enhances the robustness of the measurement.

[0020] Another challenge with the spectroscopic ellipsometry process is that the measurement only provides the thickness, refractive index, and extinction coefficient at a single point along sample 108, since the incident beam strikes the sample at that one point. Therefore, the thickness, refractive index, and extinction coefficient at other points along sample 108 are unknown, and variations in thickness, refractive index, and extinction coefficient along the sample are also unknown.

[0021] In some cases, the distributions of thickness, refractive index, and extinction coefficient of sample 108 across its surface can be determined by scanning the spectroscopic ellipsometer across the surface of the sample 108. However, scanning can be slow, and environmental variations during scanning can reduce the precision of the measurements.

[0022] In various embodiments of the present disclosure, heterodyne reflectometry is performed in two dimensions using the heterodyne common-path interferometry process to simultaneously determine the distributions of thickness, refractive index, and extinction coefficient of sample 108 across its surface (e.g., without having to perform a scan across the surface of sample 108). This allows for increased speed and precision in determining the distributions of thickness, refractive index, and extinction coefficient of sample 108.

[0023] Fig. Figure 3 shows a block diagram of 300 of some embodiments of the device of Fig. 1, in which a beam expander 202 is arranged between the beam splitter 104 and the sample 108 and the second light sensor 116 has a plurality of photodetectors.

[0024] For example, the second light sensor 116 has a pixel array with a plurality of pixels, each pixel containing a photodetector (e.g., a first pixel contains a first test photodetector 206, and a second pixel contains a second test photodetector 208). In some embodiments, the second light sensor 116 is an image sensor, such as a CCD camera (CCD: charge-coupled device), a CMOS camera (CMOS: complementary metal-oxide semiconductor), or the like.

[0025] The source beam 130 comprises a plurality of beams (e.g., a first beam 130a and a second beam 130b). A first portion of the beams from the source beam 130 is reflected by the beam splitter 104, producing beams (e.g., a first beam 134a and a second beam 134b) of the splitter-reflected beam 134. The beams of the splitter-reflected beam 134 are polarized by the first analyzer 110, producing beams (e.g., a first beam 140a and a second beam 140b) of the reference beam 140. The first light sensor 114 measures the intensity of the beams of the reference beam 140 over time. For example, beam 140a and beam 140b strike a reference photodetector 204 of the first light sensor 114, and the reference photodetector 204 measures the intensity signals of beam 140a and beam 140b, which is represented by the reference beam intensity signal I ref in Fig. 4 is shown.

[0026] A second portion of the rays from the source beam 130 is transmitted by the beam splitter 104, producing rays (e.g., a first ray 132a and a second ray 132b) from the incident beam 132. The beam expander 202 expands and collimates the rays of the incident beam 132, producing a expanded incident beam 220 with the expanded and collimated rays (e.g., a first ray 220a and a second ray 220b). For example, the beam expander 202 increases the distance between ray 132a and ray 132b and collimates these rays, producing ray 220a and ray 220b, respectively. The extended incident beam 220 strikes the sample 108 at a plurality of points along the sample 108, such that a surface of the sample 108 is captured by the extended incident beam 220.For example, the first ray 220a of the stretched incident beam 220 strikes the sample 108 at a first point 210 along the sample 108, and the second ray 220b of the stretched incident beam 220 strikes the sample 108 at a second point 212 along the sample 108, which is spaced apart from the first point 210.

[0027] Sample 108 reflects portions of the stretched incident beam 220 at multiple points along sample 108. Thus, the sample-reflected beam 136 comprises multiple rays (e.g., a first ray 136a and a second ray 136b). For example, due to the reflection of the portion of the stretched incident beam 220 at the first point 210, ray 136a emerges at the first point 210 along sample 108. Similarly, due to the reflection of the portion of the stretched incident beam 220 at the second point 212, ray 136b emerges at the second point 212 along sample 108.

[0028] The beams of the sample-reflected beam 136 are polarized by the second analyzer 112, generating beams (e.g., a first beam 138a and a second beam 138b) of the test beam 138. The second light sensor 116 measures the intensity of the beams of the test beam 138 over time. For example, beam 138a strikes the first test photodetector 206 of the second light sensor 116, and the first test photodetector 206 measures the intensity signal of beam 138a, which is represented by a first test beam intensity signal I. test-1 in Fig. Figure 4 is shown. Similarly, beam 138b strikes the second test photodetector 208 of the second light sensor 116, and the second test photodetector 208 measures the intensity signal of beam 138b, which is represented by a second test beam intensity signal I. test-2 in Fig. 4 is shown.

[0029] The characterization circuit 118 determines the phases of the test intensity signals measured by the photodetectors of the first light sensor 114. For example, the characterization circuit 118 determines a phase φ test-1 of the test intensity signal I test-1 , which is measured with the first test photodetector 206 of the second light sensor 116 (which indicates the intensity of the first beam 138a of the test beam 138) and a phase φ test-2 of the test intensity signal I test-2 , which is measured with the second test photodetector 208 of the second light sensor 116 (which indicates the intensity of the second beam 138b of the test beam 138).

[0030] The characterization circuit 118 determines the phase differences between the phases of the intensity signals and the phase of the reference intensity signal. For example, the characterization circuit 118 determines a phase difference (φ diff-1 between the phase (φtest-1 of the intensity signal I test-1 of the first beam 138a of the test beam bundle 138 and the phase φ ref of the intensity signal I ref of the reference beam 140. In addition, the characterization circuit 118 determines a phase difference (φ). diff-2 between the phase φ test-2 of the intensity signal I test-2 of the second beam 138b of the test beam bundle 138 and the phase φ ref of the intensity signal I ref of the reference beam 140.

[0031] The characterization circuit 118 determines the thickness, refractive index, and extinction coefficient of the sample 108 in a plurality of regions along the sample 108 based on the phase differences between the phases of the intensity signals and the phase of the reference intensity signal. For example, the characterization circuit 118 determines the thickness, refractive index, and extinction coefficient of the layer(s) of the sample 108 in a first region along the sample 108 (in which the first point 210 is located) based on the first phase difference φ. diff-1 between the phase φ test-1 of the intensity signal I test-1 of the first beam 138a of the test beam bundle 138 and the phase φ ref of the intensity signal I refof the reference beam 140. In addition, the characterization circuit 118 determines the thickness, refractive index and extinction coefficient of the layer(s) of the sample 108 in the second region along the sample 108 (in which the second point 212 is located) on the basis of the second phase difference φ diff-2 between the phase φ test-2 of the intensity signal I test-2 of the second beam 138b of the test beam bundle 138 and the phase φ ref of the intensity signal I ref of the reference beam 140.

[0032] By using the beam expander 202 between the beam splitter 104 and the sample 108, and by using the multiple photodetectors on the second light sensor 116, the distributions of thickness, refractive index, and extinction coefficient of the sample 108 can be determined simultaneously across its surface. This allows for increased speed and precision in determining the distributions of thickness, refractive index, and extinction coefficient of the sample 108.

[0033] The beams of Fig. Although 2 are represented as beams with two rays, the second light sensor 116 of Fig. Figure 2 is represented as a light sensor with two photodetectors, but it is understood that the beams may each contain a different number of beams and the second light sensor 116 may contain a different number of photodetectors or pixels.

[0034] Fig. Figure 5 shows a diagram 500 of some embodiments of the distributions of thickness, refractive index and extinction coefficient for a single layer of sample 108.

[0035] In the embodiments described in Fig. As shown in Figure 5, the second light sensor 116 has four pixels, and therefore four measurements (corresponding to the four areas along the sample 108) are performed with the four photodetectors of the second light sensor 116.The distributions include, for example, the following: a first refractive index n1, a first extinction coefficient k1, and a first thickness t1, corresponding to a first region along the sample 108; a second refractive index n2, a second extinction coefficient k2, and a second thickness t2, corresponding to a second region along the sample 108 except the first region in a first direction 502; a third refractive index n3, a third extinction coefficient k3, and a third thickness t3, corresponding to a third region along the sample 108 except the first region in a second direction 504, which is transverse to the first direction 502; and a fourth refractive index n4, a fourth extinction coefficient k4, and a fourth thickness t4, corresponding to a fourth region along the sample 108 except the second region in the second direction 504 and except the third region in the first direction 502.

[0036] The in Fig. Although the simplified embodiment shown in Figure 5 demonstrates properties measured in four areas along the sample 108, it is understood that more measurements can be carried out for a larger number of areas along the sample 108 in order to increase the resolution of the distributions.

[0037] Fig. Figure 6 shows a block diagram of 600 of some embodiments of the device of Fig. 3, in which the characterization circuit 118 comprises a first phase measurement circuit 602, a second phase measurement circuit 604, a phase difference circuit 606 and a computing circuit 608.

[0038] The first phase measurement circuit 602 is connected to the first light sensor 114. For example, one input of the first phase measurement circuit 602 is connected to the output of the first light sensor 114. The second phase measurement circuit 604 is connected to the second light sensor 116. For example, one input of the second phase measurement circuit 604 is connected to the output of the second light sensor 116. The phase difference circuit 606 is connected to the first phase measurement circuit 602 and the second phase measurement circuit 604. For example, one input of the phase difference circuit 606 is connected to an output of the first phase measurement circuit 602, and a second input of the phase difference circuit 606 is connected to an output of the second phase measurement circuit 604. The computing circuit 608 is connected to the phase difference circuit 606. For example, one input of the computing circuit 608 is connected to an output of the phase difference circuit 606.

[0039] The first phase measurement circuit 602 receives the reference intensity signal I ref from the reference photodetector 204 of the first light sensor 114 and determines the phase φ ref of the reference intensity signal I ref The second phase measurement circuit 604 receives the test intensity signals (e.g., I). test-1 , I test-2 ) from the photodetectors of the second light sensor 116 and determines the phases (e.g. φ) test-1 , φ test-2 ) of the test intensity signals. The phase difference circuit 606 receives the phases (e.g., φ). test-1 , φ test-2 ) the test intensity signals and the phase of the reference intensity signal I ref and determines the phase differences (e.g. φ) diff-1 , φ diff-2 ) between the phases of the test intensity signals (e.g. φ) test-1 , φ test-2 ) and the phase of the reference intensity signal φ ref The 608 computing circuit receives the phase differences (e.g., φ). diff-1 , φ diff-2) and determines the thickness, refractive index and extinction coefficient of the layer(s) of sample 108 in the majority of areas along sample 108 based on the phase differences.

[0040] In some embodiments, the heterodyne light source 102 further comprises a laser light source 610, an electro-optic modulator (EO modulator) 612, an amplifier 614, and a function generator (FG) 616. The laser light source 610 generates a laser beam 620 comprising a plurality of beams (e.g., a first beam 620a and a second beam 620b). The laser beam 620 contains s- and p-polarized light. The EO modulator 612 receives the laser beam 620 and a modulation signal 622 and modulates the laser beam 620 (e.g., the phase difference between the s- and p-polarized light of the laser beam 620) according to a modulation frequency of the modulation signal 622, thereby generating the source beam 130. The frame rate of the second light sensor 116 is at least twice the modulation frequency.The function generator 616 generates a basic signal 624, and the amplifier 614 amplifies the basic signal 624, thereby creating the modulation signal 622.

[0041] In some embodiments, the linear polarization direction of the laser beam 620 is set to a 45° angle to a first axis (e.g. into the sheet); a first axis of the EO modulator 612 is defined as an axis running along the first axis; a first axis of the sample 108 is defined as an axis running along the first axis; and transmission axes of the analyzers 110, 112 are set to a 45° angle to the first axis.

[0042] Fig. Figure 7 shows a block diagram of some embodiments of the device of Fig. 6, which continues to have a first actuator 702 and a second actuator 708.

[0043] Sample 108 is placed on the first actuator 702. The second analyzer 112 and the second light sensor 116 are placed on the second actuator 708.

[0044] The first actuator 702 rotates the sample 108 about an axis 704, as indicated by an arrow 706, to adjust the angle of incidence of the stretched beam 220 striking the sample 108. The second actuator 708 rotates the second analyzer 112 and the second light sensor 116 about the axis 704 to adjust the angle of the second analyzer 112 and the second light sensor 116 based on the angle of the sample 108 (e.g., based on a reflection angle of the sample-reflected beam 136) such that the sample-reflected beam 136 passes through the second analyzer 112 and the test beam 138 strikes the second light sensor 116.In some embodiments, the second actuator 708 rotates the second analyzer 112 and the second light sensor 116 about the axis 704 by moving them along a transport path 710, as indicated by an arrow 712, and by rotating them about an axis 714, as indicated by an arrow 716. In some embodiments, the axis 704 runs along the center of a surface of the sample 108.

[0045] Fig. Figure 8 shows a block diagram of some embodiments of the device of Fig. 6, which also has a mirror 802 and, in addition to the first actuator 702, a second actuator 804 and a third actuator 806.

[0046] The mirror 802 is arranged between the beam splitter 104 and the beam expander 202. The beam expander 202 is arranged between the mirror 802 and the sample 108. The sample 108 is arranged on the first actuator 702. The beam expander 202 and the third actuator 806 are arranged on the second actuator 804. The mirror 802 is arranged on the third actuator 806.

[0047] The incident beam 132 strikes the mirror 802, and the mirror 802 reflects the incident beam 132 to the beam expander 202. The first actuator 702 rotates the sample 108 about the axis 704 (as shown by arrow 706), the second actuator 804 rotates the beam expander 202 and the third actuator 806 (and thus the mirror 802) about the axis 704 (as shown by arrow 814), and the third actuator 806 rotates the mirror 802 about an axis 809 (as shown by arrow 808) to adjust the angle of incidence of the expanded beam 220 striking the sample 108 and to direct the sample-reflected beam 136 to the second analyzer 112 and the second light sensor 116, so that the Sample-reflected beam 136 passes through the second analyzer 112 and the test beam 138 hits the second light sensor 116.In some embodiments, the second actuator 804 rotates the beam expander 202 and the third actuator 806 about the axis 704 by moving them along a transport path 810 (as indicated by arrow 812) and by rotating them about the axis 809 (as indicated by arrow 814). In some embodiments, the axis 809 runs along the center of a surface of the mirror 802. In some embodiments, the positions of the second analyzer 112 and the second light sensor 116 are fixed.

[0048] Fig. Figure 9 shows a block diagram of some embodiments of the device of Fig. 6, which additionally includes the mirror 802, the actuator 804 and the actuator 708.

[0049] Mirror 802 is arranged between beam splitter 104 and beam expander 202. Beam expander 202 is arranged between mirror 802 and sample 108. Beam expander 202 and actuator 806 are arranged on actuator 804. Mirror 802 is arranged on actuator 806. The second analyzer 112 and the second light sensor 116 are arranged on actuator 708.

[0050] The actuator 804 rotates the beam expander 202 and the actuator 806 (and thus the mirror 802) about the axis 704 (as shown by the arrow 814), and the actuator 806 rotates the mirror 802 about the axis 809 (as shown by the arrow 808) to adjust the angle of incidence of the expanded beam 220 striking the sample 108. The actuator 708 rotates the second analyzer 112 and the second light sensor 116 about the axis 704 in order to adjust the angle of the second analyzer 112 and the second light sensor 116 based on the angle of incidence of the extended incident beam 220 (e.g., based on the angle of reflection of the sample-reflected beam 136) such that the sample-reflected beam 136 passes through the second analyzer 112 and the test beam 138 strikes the second light sensor 116. In some embodiments, the position of the sample 108 is fixed.

[0051] The Fig. 10, Fig. 11, Fig. 12 to Fig. Figure 13 shows sectional views 1000, 1100, 1200 and 1300 of some embodiments of specimen 108.

[0052] In some embodiments, the sample 108 is arranged on a sample holder 1004, or it is supported by this holder. In some embodiments (e.g., in Fig. (as shown in Figure 10) sample 108 is an “independent” single thin film 1002. In some other embodiments (e.g., those shown in Figure 10), the sample 108 is an “independent” single thin film 1002. Fig. As shown in Figure 11, sample 108 comprises a single thin film 1002 and a substrate 1102 on which the single thin film 1002 is arranged. In some further embodiments (e.g., those shown in Figure 11), the sample 108 comprises a single thin film 1002 and a substrate 1102 on which the single thin film 1002 is arranged. Fig. As shown in Figure 12, sample 108 has a plurality of independent thin films (e.g., thin film 1002, thin film 1202 beneath thin film 1002, and thin film 1204 beneath thin film 1202). In some further embodiments (e.g., shown in Figure 12), the sample 108 has a plurality of independent thin films (e.g., thin film 1002, thin film 1202, thin film 1204 ... Fig. As shown in Figure 13, sample 108 comprises a plurality of thin films (e.g., thin films 1002, 1202, 1204) and the substrate 1102 on which the thin films are arranged. In some embodiments, the independent layers can be or form a pellicle for photolithography, e.g., EUV photolithography (EUV: extreme ultraviolet). In some embodiments, the layers on the substrate can be conductive layers, semiconductor layers, dielectric layers, or the like.

[0053] Fig. Figure 14 shows a diagram 1400 of some embodiments of distributions of thickness, refractive index and extinction coefficient for a plurality of layers of sample 108.

[0054] In the embodiments described in Fig. As shown in Figure 14, the second light sensor 116 has four pixels, and therefore four measurements (corresponding to the four regions along each of the three layers of the sample 108) are performed with the four photodetectors of the second light sensor 116. The distributions in the first layer, for example, include four refractive indices n1 to n4, four extinction coefficients k1 to k4, and four thicknesses t1 to t4. Similarly, the distributions in the second layer include four refractive indices n5 to n8, four extinction coefficients k5 to k8, and four thicknesses t5 to t8. Similarly, the distributions in the third layer include four refractive indices n9 to n 12 , four extinction coefficients k9 to k 12 and four thicknesses t9 to t 12 .

[0055] The in Fig. Although the simplified embodiment shown in Figure 14 depicts properties measured in four regions along a three-layer sample, it is understood that more measurements can be performed for a larger number of regions along the sample 108 to increase the resolution of the distributions. It is also understood that the sample can have a different number of layers.

[0056] The Fig. 15, Fig. 16 to Fig. Figure 17 shows block diagrams 1500, 1600 and 1700 of some embodiments of a method for determining the thickness, refractive index and extinction coefficient of a sample 108. Fig. 18, Fig. 19 to Fig. Figure 20 shows block diagrams 1800, 1900 and 2000 of some further embodiments of a method for determining the thickness, refractive index and extinction coefficient of a sample 108. Fig. 21, Fig. 22 to Fig. Figure 23 shows block diagrams 2100, 2200 and 2300 of some further embodiments of a method for determining the thickness, refractive index and extinction coefficient of a sample 108. Fig. 15, Fig. 16, Fig. 17, Fig. 18, Fig. 19, Fig. 20, Fig. 21, Fig. 22 to Fig. Figures 23 are described for procedures, but it is understood that the structures revealed in these figures are not limited to these procedures, but can be used as structures independent of the procedure.

[0057] First, a first measurement is taken using a first source beam 130-1 of heterodyne light with a first angle of incidence. In some embodiments (e.g., those in the Fig. 15, Fig. 16 to Fig. (as shown in Figure 17) the angle of incidence (e.g., the angle between the rays of the first source beam 130-1 and the perpendicular to the surface of the sample 108) is set to the first angle of incidence by rotating the sample 108 with the actuator 702 about the axis 704 to a first sample position. Based on the first sample position, the analyzer 112 and the light sensor 116 are rotated with the actuator 708 about the axis 704 to a first sensor position. In some further embodiments (which are shown, for example, in the Fig. 18, Fig. 19 to Fig. (as shown in Figure 20) the angle of incidence is set to the first angle of incidence by rotating the sample 108 with the actuator 702 about the axis 704 to the first sample position, rotating the beam expander 202 and the mirror 802 with the actuator 804 about the axis 704 to a first source position, and rotating the mirror 802 with the actuator 806 about the axis 809 to a first mirror position. In some further embodiments (which are shown, for example, in the Fig. 21, Fig. 22 to Fig. (as shown in Figure 23) the angle of incidence is set to the first angle of incidence by rotating the beam expander 202 and the mirror 802 with the actuator 804 about the axis 704 to a first source position, and by rotating the mirror 802 with the actuator 806 about the axis 809 to the first mirror position. Based on the first source position, the analyzer 112 and the light sensor 116 are rotated with the actuator 708 about the axis 704 to a first sensor position.

[0058] Once the actuator positions have been set, a heterodyne light source 102 generates the first source beam 130-1 to a sample 108, which is a first test layer (e.g. layer 1002 of the Fig. 10, Fig. 11, Fig. 12 to Fig. 13). The first source beam 130-1 contains s- and p-polarized light, with a phase difference between the s- and p-polarized light being modulated (e.g., according to a modulation frequency of a modulation signal).

[0059] A beam splitter 104 reflects a first part of the first source beam 130-1, creating a first splitter-reflected beam 134-1. The first analyzer 110 polarizes the first splitter-reflected beam 134-1, creating a first reference beam 140-1. The first light sensor 114 measures an intensity signal of the first reference beam 140-1. The first phase measurement circuit 602 determines a phase of the intensity signal of the first reference beam 140-1.

[0060] The beam splitter 104 allows a second part of the first source beam 130-1 to pass through, thereby creating a first incident beam 132-1. A beam expander 202 expands and collimates the first incident beam 132-1, thereby creating a first expanded incident beam 220-1. In some embodiments (e.g., those described in the following) Fig. (18 to 20 and 21 to 23 are shown) the mirror 802 reflects the first stretched incident beam 220-1 to the beam stretcher 202 and the sample 108.

[0061] The first elongated incident beam 220-1 strikes the sample 108 at a first angle of incidence. Part of the first elongated incident beam 220-1 is reflected by the sample 108, resulting in a first sample-reflected beam 136-1.

[0062] A second analyzer 112 polarizes the first sample-reflected beam 136-1, generating a first test beam 138-1. Photodetectors (e.g., pixels) of a second light sensor 116 measure the intensity of the first test beam 138-1. For example, a first test photodetector 206 measures a first intensity signal of the first test beam 138-1 (corresponding, for example, to a first beam of the first test beam emerging from a first region along the sample), and a second pixel measures a second intensity signal of the first test beam 138-1 (corresponding, for example, to a second beam of the first test beam emerging from a second region along the sample). The second phase measurement circuit 604 determines the phases of the intensity signals of the first test beam 138-1.For example, the second phase measurement circuit 604 determines a phase of the first intensity signal of the first test beam 138-1 (which is measured with the test photodetector 206) and a phase of the second intensity signal of the first test beam 138-1 (which is measured with the test photodetector 208).

[0063] The phase difference circuit 606 determines a phase difference between a phase of the intensity signal of the first test beam 138-1 and a phase of the intensity signal of the first reference beam 140-1 (e.g., a first phase difference). For example, the phase difference circuit 606 determines a phase difference between a phase of the intensity signal of the first test beam 138-1 (measured with the test photodetector 206) and a phase of the intensity signal of the first reference beam 140-1, and it determines a phase difference between a phase of the second intensity signal of the first test beam 138-1 (measured with the test photodetector 208) and a phase of the intensity signal of the first reference beam 140-1.

[0064] Then a second measurement is taken using a second source beam 130-2 of heterodyne light with a second angle of incidence. In some embodiments (e.g., those in the Fig. 15, Fig. 16 to Fig. (as shown in Figure 17) the angle of incidence is adjusted to the second angle of incidence by rotating the sample 108 with the actuator 702 about the axis 704 to a second sample position. Based on the second sample position, the analyzer 112 and the light sensor 116 are rotated with the actuator 708 about the axis 704 to a second sensor position. In some further embodiments (which are shown, for example, in the Fig. 18, Fig. 19 to Fig. (as shown in Figure 20) the angle of incidence is adjusted to the second angle of incidence by rotating the sample 108 with the actuator 702 about the axis 704 to the second sample position, rotating the beam expander 202 and the mirror 802 with the actuator 804 about the axis 704 to a second source position, and rotating the mirror 802 with the actuator 806 about the axis 809 to a second mirror position. In some further embodiments (which are shown, for example, in the Fig. 21, Fig. 22 to Fig. (as shown in Figure 23) the angle of incidence is adjusted to the second angle of incidence by rotating the beam expander 202 and the mirror 802 with the actuator 804 about the axis 704 to a second source position, and by rotating the mirror 802 with the actuator 806 about the axis 809 to the second mirror position. Based on the second source position, the analyzer 112 and the light sensor 116 are rotated with the actuator 708 about the axis 704 to a second sensor position.

[0065] Once the actuator positions have been set, the heterodyne light source 102 generates the second source beam 130-2 to the sample 108.

[0066] The beam splitter 104 reflects a first part of the second source beam 130-2, creating a second splitter-reflected beam 134-2. The first analyzer 110 polarizes the second splitter-reflected beam 134-2, creating a second reference beam 140-2. The first light sensor 114 measures an intensity signal of the second reference beam 140-2. The first phase measurement circuit 602 determines a phase of the intensity signal of the second reference beam 140-2.

[0067] The beam splitter 104 allows a second part of the second source beam 130-2 to pass through, thereby creating a second incident beam 132-2. The beam expander 202 expands and collimates the second incident beam 132-2, thereby creating a second expanded incident beam 220-2. In some embodiments (e.g., those described in the following): Fig. (18 to 20 and 21 to 23 are shown) the mirror 802 reflects the second stretched incident beam 220-2 to the beam stretcher 202 and the sample 108.

[0068] The second elongated incident beam 220-2 strikes sample 108 at a second angle of incidence that differs from the first. Part of the second elongated incident beam 220-2 is reflected by sample 108, resulting in a second sample-reflected beam 136-2.

[0069] The second analyzer 112 polarizes the second sample-reflected beam 136-2, thereby generating a second test beam 138-2. Pixels of the second light sensor 116 measure the intensity of the second test beam 138-2. The second phase measurement circuit 604 determines the phases of the intensity signals of the second test beam 138-2.

[0070] The phase difference circuit 606 determines a phase difference between a phase of the intensity signal of the second test beam 138-2 and a phase of the intensity signal of the second reference beam 140-2 (e.g. a second phase difference).

[0071] Then a third measurement is taken using a third source beam 130-3 of heterodyne light and a third angle of incidence. In some embodiments (e.g., those in the Fig. 15, Fig. 16 to Fig. (as shown in Figure 17) the angle of incidence is adjusted to the third angle of incidence by rotating the sample 108 with the actuator 702 about the axis 704 to a third sample position. Based on the third sample position, the analyzer 112 and the light sensor 116 are rotated with the actuator 708 about the axis 704 to a third sensor position. In some further embodiments (which are shown, for example, in the Fig. 18, Fig. 19 to Fig. (as shown in Figure 20) the angle of incidence is adjusted to the third angle of incidence by rotating the sample 108 with the actuator 702 about the axis 704 to the third sample position, rotating the beam expander 202 and the mirror 802 with the actuator 804 about the axis 704 to a third source position, and rotating the mirror 802 with the actuator 806 about the axis 809 to a third mirror position. In some further embodiments (which are shown, for example, in the Fig. 21, Fig. 22 to Fig. (as shown in Figure 23) the angle of incidence is adjusted to the third angle of incidence by rotating the beam expander 202 and the mirror 802 with the actuator 804 about the axis 704 to a third source position, and by rotating the mirror 802 with the actuator 806 about the axis 809 to the third mirror position. Based on the third source position, the analyzer 112 and the light sensor 116 are rotated with the actuator 708 about the axis 704 to a third sensor position.

[0072] Once the actuator positions have been set, the heterodyne light source 102 generates the third source beam 130-3 to the sample 108.

[0073] The beam splitter 104 reflects a first part of the third source beam 130-3, creating a third splitter-reflected beam 134-3. The first analyzer 110 polarizes the third splitter-reflected beam 134-3, creating a third reference beam 140-3. The first light sensor 114 measures an intensity signal of the third reference beam 140-3. The first phase measurement circuit 602 determines a phase of the intensity signal of the third reference beam 140-3.

[0074] The beam splitter 104 allows a second part of the third source beam 130-3 to pass through, thereby creating a third incident beam 132-3. The beam expander 202 expands and collimates the third incident beam 132-3, thereby creating a third expanded incident beam 220-3. In some embodiments (e.g., those described in the following): Fig. (18 to 20 and 21 to 23 are shown) the mirror 802 reflects the third stretched incident beam 220-3 to the beam stretcher 202 and the sample 108.

[0075] The third elongated incident beam 220-3 strikes sample 108 at a third angle of incidence, which differs from the first and second angles of incidence. Part of the third elongated incident beam 220-3 is reflected by sample 108, resulting in a third sample-reflected beam 136-3.

[0076] The second analyzer 112 polarizes the third sample-reflected beam 136-3, thereby generating a third test beam 138-3. Pixels of the second light sensor 116 measure the intensity of the third test beam 138-3. The second phase measurement circuit 604 determines the phases of the intensity signals of the third test beam 138-3.

[0077] The phase difference circuit 606 determines a phase difference between a phase of the intensity signal of the third test beam 138-3 and a phase of the intensity signal of the third reference beam 140-3 (e.g. a third phase difference).

[0078] The computing circuit 608 determines a thickness, a refractive index and an extinction coefficient of the sample 108 on the basis of the first phase difference (which corresponds to the first angle of incidence), the second phase difference (which corresponds to the second angle of incidence) and the third phase difference (which corresponds to the third angle of incidence).For example, the computing circuit 608 determines the thickness, refractive index and extinction coefficient of the layer(s) of the sample 108 in the first region along the sample on the basis of the phase difference between the phase of the first intensity signal of the first test beam 138-1 (corresponding to the test photodetector 206) and the phase of the intensity signal of the first reference beam 140-1, the phase difference between the phase of the first intensity signal of the second test beam 138-2 (corresponding to the test photodetector 206) and the phase of the intensity signal of the second reference beam 140-2 and the phase difference between the phase of the first intensity signal of the third test beam 138-3 (corresponding to the test photodetector 206) and the phase of the intensity signal of the third reference beam 140-3.Similarly, the computing circuit 608 determines the thickness, refractive index and extinction coefficient of the layer(s) of the sample 108 in the second region along the sample on the basis of the phase difference between the phase of the second intensity signal of the first test beam 138-1 (corresponding to the test photodetector 208) and the phase of the intensity signal of the first reference beam 140-1, the phase difference between the phase of the second intensity signal of the second test beam 138-2 (corresponding to the test photodetector 208) and the phase of the intensity signal of the second reference beam 140-2 and the phase difference between the phase of the second intensity signal of the third test beam 138-3 (corresponding to the test photodetector 208) and the phase of the intensity signal of the third reference beam 140-3.

[0079] To determine the thickness, refractive index, and extinction coefficient distributions of a sample with N layers, some embodiments perform 3xN phase difference measurements at 3xN different angles of incidence. For example, to determine the thickness, refractive index, and extinction coefficient distributions of a three-layer sample, phase difference measurements are performed at nine different angles of incidence. Furthermore, all nine different phase difference measurements for the three-layer sample are used to determine the thickness, refractive index, and extinction coefficient of each layer in the sample.For example, the thickness, refractive index, and extinction coefficient of the first layer of the sample are determined based on all nine different phase difference measurements; the thickness, refractive index, and extinction coefficient of the second layer of the sample are determined based on all nine different phase difference measurements; and the thickness, refractive index, and extinction coefficient of the third layer of the sample are determined based on all nine different phase difference measurements. In some embodiments, the angles of incidence are in a range of 0° to 90°, 10° to 80°, or another suitable range.

[0080] Fig. Figure 24 shows a flowchart of some embodiments of a method 2400 for determining the distributions of the thickness, refractive index, and extinction coefficient of the layer(s) of a sample across a surface of the sample. Although the method 2400 is presented and described below as a series of steps or events, it is understood that the sequence of these steps or events shown should not be interpreted as restrictive. For example, the steps may be performed in a different order than shown, and / or they may occur concurrently with other steps or events than those shown and / or described here. Furthermore, it may not be necessary to implement all of the steps shown to implement one or more aspects or embodiments of the description.Furthermore, one or more of the steps shown can be carried out in one or more separate steps and / or phases.

[0081] In block 2402, a first source beam of heterodyne light is generated for a sample using a heterodyne light source such that the first source beam hits the sample at a first angle of incidence.

[0082] In a block 2404, the first source beam is polarized with a first analyzer to produce a first reference beam, and the part of the first source beam reflected by the sample is polarized with a second analyzer to produce a first test beam.

[0083] In block 2406, an intensity signal of the first reference beam is measured with a reference photodetector, and intensity signals of the first test beam are measured with test photodetectors.

[0084] In block 2408, phase differences between the phases of the first test intensity signals and a phase of the first reference intensity signal are determined. Fig. 15, Fig. 18 and Fig. 21 show block diagrams 1500, 1800, 2100 of some embodiments, which correspond to blocks 2402, 2404, 2406, 2408.

[0085] In a block 2410, a second source beam of heterodyne light is generated for the sample using a heterodyne light source such that the second source beam hits the sample at a second angle of incidence.

[0086] In a block 2412, the second source beam is polarized with the first analyzer to create a second reference beam, and the part of the second source beam reflected by the sample is polarized with the second analyzer to create a second test beam.

[0087] In block 2414, an intensity signal of the second reference beam is measured with the reference photodetector, and intensity signals of the second test beam are measured with the test photodetectors.

[0088] In block 2416, phase differences between phases of the second test intensity signals and a phase of the second reference intensity signal are determined. Fig. 16, Fig. 19 and Fig. Figure 22 shows block diagrams 1600, 1900, 2200 of some embodiments, which correspond to blocks 2410, 2412, 2414, 2416.

[0089] In block 2418, the phase difference measurements are repeated for further angles of incidence based on the number of layers in the sample. Fig. 17, Fig. 20 and Fig. Figure 23 shows block diagrams 1700, 2000, 2300 of some embodiments corresponding to block 2418.

[0090] In block 2420, the distributions of thickness, refractive index, and extinction coefficient of the layer(s) of the sample are determined across a surface of the sample based on the phase differences. Fig. 5 and Fig. Figure 14 shows diagrams 500 and 1400 of some embodiments of the distributions of the thickness, refractive index and extinction coefficient of the layer(s) of the sample across a surface of the sample.

[0091] Thus, in some embodiments, the present disclosure relates to a method comprising generating a first source beam of heterodyne light to a first test layer such that the first source beam strikes the first test layer at a first angle of incidence. The method further comprises polarizing the first source beam, thereby generating a first reference beam, and polarizing a portion of the first source beam reflected from the first test layer, thereby generating a first test beam. The method further comprises measuring an intensity signal of the first reference beam and measuring an intensity signal of the first test beam. The method further comprises determining a difference between a phase of the intensity signal of the first test beam and a phase of the intensity signal of the first reference beam.The method further comprises determining a refractive index, an extinction coefficient, and a thickness of the first test layer based on the difference between the phase of the intensity signal of the first test beam and the phase of the intensity signal of the first reference beam. In some embodiments, the method further comprises: generating a second source beam of heterodyne light to the first test layer such that the second source beam strikes the first test layer at a second angle of incidence different from the first angle of incidence; polarizing the second source beam, thereby creating a second reference beam, and polarizing a portion of the second source beam reflected from the first test layer, thereby creating a second test beam; measuring an intensity signal of the second reference beam; and measuring an intensity signal of thesecond test beam; determining a difference between a phase of the intensity signal of the second test beam and a phase of the intensity signal of the second reference beam; and determining the refractive index, extinction coefficient, and thickness of the first test layer, again based on the difference between the phase of the intensity signal of the second test beam and the phase of the intensity signal of the second reference beam. In some embodiments, the method further comprises: generating a third source beam of heterodyne light to the first test layer such that the third source beam strikes the first test layer at a third angle of incidence different from the first and second angles of incidence; polarizing the third source beam, thereby creating a third reference beam; and polarizing a portion of the third source beam that isthe first test layer is reflected, thereby creating a third test beam; measuring an intensity signal of the third reference beam and measuring an intensity signal of the third test beam; determining a difference between a phase of the intensity signal of the third test beam and a phase of the intensity signal of the third reference beam; and determining the refractive index, extinction coefficient, and thickness of the first test layer, again based on the difference between the phase of the intensity signal of the third test beam and the phase of the intensity signal of the third reference beam. In some embodiments, the method further includes: adjusting the angle of incidence of the first source beam to the first angle of incidence; adjusting the angle of incidence of the second source beam to the second angle of incidence; and adjusting the angle of incidence of the thirdsource beam beam to the third angle of incidence. In some embodiments, measuring the intensity signal of the first test beam beam comprises measuring the intensity signal of a first beam of the first test beam beam and measuring the intensity signal of a second beam of the first test beam beam. In some embodiments, determining the difference between the phase of the intensity signal of the first test beam beam and the phase of the intensity signal of the first reference beam beam comprises: determining a difference between a phase of the intensity signal of the first beam of the first test beam beam and the phase of the intensity signal of the first reference beam beam; and determining a difference between a phase of the intensity signal of the second beam of the first test beam beam and the phase of the intensity signal of the first reference beam beam. In some embodiments, theDetermining the refractive index, extinction coefficient, and thickness of the first test layer based on the difference between the phase of the intensity signal of the first test beam and the phase of the intensity signal of the first reference beam: Determining the refractive index, extinction coefficient, and thickness of the first test layer in a first region along the first test layer based on the difference between the phase of the intensity signal of the first beam of the first test beam and the phase of the intensity signal of the first reference beam; and Determining the refractive index, extinction coefficient, and thickness of the first test layer in a second region along the first test layer, different from the first region, based on the difference between the phase of the intensity signal of the second beam of the first test beam and the phase of the intensity signal of the first reference beam.In some embodiments, the method further comprises determining a refractive index, an extinction coefficient and a thickness of a second test layer beneath the first test layer based on the difference between the phase of the intensity signal of the first test beam and the phase of the intensity signal of the first reference beam.

[0092] In further embodiments, the present disclosure relates to a method comprising generating, with a heterodyne light source, a first source beam of heterodyne light onto a sample having a first test layer. The method further comprises polarizing, with a first analyzer, a first portion of the first source beam, thereby generating a first reference beam. The method further comprises measuring, with a first light sensor, an intensity signal of the first reference beam. The method further comprises stretching, with a beam stretcher, a second portion of the first source beam, thereby generating a stretched beam. The stretched beam strikes the first test layer at a first angle of incidence, and a portion of the stretched beam is reflected by the first test layer, thereby generating a first reflected beam.The method further comprises polarizing the first reflected beam with a second analyzer, thereby generating a first test beam. The method further comprises measuring a first intensity signal of the first test beam with a first pixel of a second light sensor; and measuring a second intensity signal of the first test beam with a second pixel of the second light sensor. The method further comprises determining a difference between a phase of the first intensity signal of the first test beam and a phase of the intensity signal of the first reference beam. The method further comprises determining a difference between a phase of the second intensity signal of the first test beam and the phase of the intensity signal of the first reference beam.The method further comprises determining the refractive index, extinction coefficient, and thickness of the first test layer in a first region along the test layer based on the difference between the phase of the first intensity signal of the first test beam and the phase of the intensity signal of the first reference beam. The method further comprises determining the refractive index, extinction coefficient, and thickness of the first test layer in a second region spaced apart from the first region along the first test layer based on the difference between the phase of the second intensity signal of the first test beam and the phase of the intensity signal of the first reference beam. In some embodiments, the second part of the first source beam is stretched and collimated by the beam stretcher such that a surface of the first test layer is captured by the stretched beam.In some embodiments, the method further comprises adjusting the first angle of incidence by rotating the first test layer about an axis; and rotating the second analyzer and the second light sensor about the axis in response to the rotation of the first test layer about the axis. In some embodiments, the method further comprises reflecting, with a mirror, the second part of the first source beam to the beam expander and the first test layer; and adjusting the first angle of incidence by rotating the first test layer, the mirror, and the beam expander about an axis.In some embodiments, the method further comprises reflecting, with a mirror, the second part of the first source beam to the beam expander and the first test layer; adjusting the first angle of incidence by rotating the mirror and the beam expander about an axis; and rotating the second analyzer and the second light sensor about the axis in response to the rotation of the mirror and the beam expander about the axis. In some embodiments, the method further comprises reflecting, with a beam splitter, the first part of the first source beam before polarizing the first part of the first source beam; and transmitting, with the beam splitter, the second part of the first source beam before expanding the second part of the first source beam.In some embodiments, the first source beam of heterodyne light is generated by producing a precursor beam with s- and p-polarized light and modulating a phase difference between the s- and p-polarized light of the precursor beam according to a modulation frequency.

[0093] In further embodiments, the present disclosure relates to a device comprising a heterodyne light source, a beam splitter, a first analyzer, a first light sensor, a beam expander, a second analyzer, a second light sensor, and a characterization circuit. The heterodyne light source is configured to generate a first source beam of heterodyne light directed to a first test layer. The beam splitter is arranged between the heterodyne light source and the first test layer and is configured to reflect a first part of the first source beam and transmit a second part of the first source beam. The first analyzer is configured to polarize the first part of the first source beam, thereby generating a first reference beam.The first light sensor is configured to measure the intensity of the first reference beam. The first analyzer is positioned between the beam splitter and the first light sensor. The beam stretcher is positioned between the beam splitter and the first test layer. The beam splitter is configured to stretch and collimate the second portion of the first source beam, producing a stretched beam. The second analyzer is configured to stretch a portion of the stretched beam reflected from the first test layer, producing a first test beam. The second light sensor contains a first and a second pixel configured to measure the intensity of the first test beam. The second analyzer is positioned between the first test layer and the second light sensor.The characterization circuit is connected to the first and second light sensors. The characterization circuit is configured to determine the difference between the phase of the intensity signal of the first test beam and the phase of the intensity signal of the first reference beam. Based on this difference, the characterization circuit determines the refractive index, extinction coefficient, and thickness of the first test layer.In some embodiments, the device further comprises: a first actuator configured to rotate the first test layer about an axis in order to set an angle of incidence at which the stretched beam of light strikes the first test layer; and a second actuator configured to rotate the second analyzer and the second light sensor about the axis.In some embodiments, the device further comprises: a mirror arranged between the beam splitter and the beam expander, configured to reflect the second part of the first source beam to the beam expander and the first test layer; a first actuator configured to rotate the first test layer about an axis; and a second actuator configured to rotate the mirror and the beam expander about the axis to set an angle of incidence at which the expanded beam strikes the first test layer.In some embodiments, the device further comprises: a mirror arranged between the beam splitter and the beam expander, configured to reflect the second part of the first source beam to the beam expander and the first test layer; a first actuator configured to rotate the mirror and the beam expander about an axis to set an angle of incidence at which the expanded beam strikes the first test layer; and a second actuator configured to rotate the second analyzer and the second light sensor about the axis.In some embodiments, the heterodyne light source includes a laser light source configured to produce a laser beam with s- and p-polarized light, and the heterodyne light source further includes a modulator configured to modulate a phase difference between the s- and p-polarized light of the laser beam.

[0094] Features of various embodiments have been described above so that those skilled in the art can better understand the aspects of the present disclosure. It should be clear to those skilled in the art that they can readily use the present disclosure as a basis for designing or modifying other methods and structures to achieve the same objectives and / or to obtain the same advantages as in the embodiments presented here. Those skilled in the art should also recognize that such equivalent interpretations do not deviate from the fundamental concept and scope of protection of the present disclosure and that they can make various changes, substitutions, and modifications without deviating from the fundamental concept and scope of protection of the present disclosure.

Claims

[1] Procedure, encompassing: Generating a first source beam of heterodyne light to a first test layer such that the first source beam strikes the first test layer at a first angle of incidence; Polarizing the first source beam, thereby creating a first reference beam, and polarizing a portion of the first source beam that is reflected by the first test layer, thereby creating a first test beam; Measuring an intensity signal of the first reference beam and measuring an intensity signal of the first test beam; Determining a difference between a phase of the intensity signal of the first test beam and a phase of the intensity signal of the first reference beam; and Determining a refractive index, an extinction coefficient and a thickness of the first test layer based on the difference between the phase of the intensity signal of the first test beam and the phase of the intensity signal of the first reference beam. [2] The method of claim 1, further comprising: Generating a second source beam of heterodyne light to the first test layer such that the second source beam strikes the first test layer at a second angle of incidence different from the first angle of incidence; Polarizing the second source beam, creating a second reference beam, and polarizing a portion of the second source beam that is reflected by the first test layer, creating a second test beam; Measuring an intensity signal of the second reference beam and measuring an intensity signal of the second test beam; Determining a difference between a phase of the intensity signal of the second test beam and a phase of the intensity signal of the second reference beam; and Determining the refractive index, extinction coefficient and thickness of the first test layer, again based on the difference between the phase of the intensity signal of the second test beam and the phase of the intensity signal of the second reference beam. [3] The method of claim 2, further comprising: Generating a third source beam of heterodyne light to the first test layer such that the third source beam strikes the first test layer at a third angle of incidence different from the first and second angles of incidence; Polarizing the third source beam, creating a third reference beam, and polarizing a portion of the third source beam that is reflected by the first test layer, creating a third test beam; Measuring an intensity signal of the third reference beam and measuring an intensity signal of the third test beam; Determining a difference between a phase of the intensity signal of the third test beam and a phase of the intensity signal of the third reference beam; and Determining the refractive index, extinction coefficient and thickness of the first test layer again on the basis of the difference between the phase of the intensity signal of the third test beam and the phase of the intensity signal of the third reference beam. [4] The method of claim 3, further comprising: Adjusting the angle of incidence of the first source beam to the first angle of incidence; Adjusting the angle of incidence of the second source beam to the second angle of incidence; and Adjusting the angle of incidence of the third source beam to the third angle of incidence. [5] Method according to any of the preceding claims, wherein measuring the intensity signal of the first test beam comprises measuring an intensity signal of a first beam of the first test beam and measuring an intensity signal of a second beam of the first test beam. [6] Method according to claim 5, wherein determining the difference between the phase of the intensity signal of the first test beam and the phase of the intensity signal of the first reference beam comprises the following: Determining a difference between the phase of the intensity signal of the first beam of the first test beam and the phase of the intensity signal of the first reference beam; and Determining a difference between the phase of the intensity signal of the second beam of the first test beam and the phase of the intensity signal of the first reference beam. [7] Method according to claim 6, wherein determining the refractive index, extinction coefficient and thickness of the first test layer based on the difference between the phase of the intensity signal of the first test beam and the phase of the intensity signal of the first reference beam comprises the following: Determining the refractive index, extinction coefficient, and thickness of the first test layer in a first region along the first test layer based on the difference between the phase of the intensity signal of the first beam of the first test beam and the phase of the intensity signal of the first reference beam; and Determining the refractive index, extinction coefficient and thickness of the first test layer in a second area different from the first along the first test layer based on the difference between the phase of the intensity signal of the second beam of the first test beam and the phase of the intensity signal of the first reference beam. [8] A method according to any of the preceding claims, further comprising: Determining a refractive index, an extinction coefficient and a thickness of a second test layer beneath the first test layer based on the difference between the phase of the intensity signal of the first test beam and the phase of the intensity signal of the first reference beam. [9] Procedures, comprehensive: Generating, using a heterodyne light source, a first source beam of heterodyne light to a sample that has a first test layer; Polarizing, with a first analyzer, a first part of the first source beam, thereby creating a first reference beam; Measuring, with a first light sensor, an intensity signal of the first reference beam; Stretching, with a beam stretcher, a second part of the first source beam, thereby creating a stretched beam, wherein the stretched beam strikes the first test layer at a first angle of incidence and part of the stretched beam is reflected by the first test layer, thereby creating a first reflected beam; Polarizing the first reflected beam with a second analyzer, thereby creating a first test beam; Measuring, with a first pixel of a second light sensor, a first intensity signal of the first test beam, and measuring, with a second pixel of the second light sensor, a second intensity signal of the first test beam; Determining a difference between a phase of the first intensity signal of the first test beam and a phase of the intensity signal of the first reference beam, and determining a difference between a phase of the second intensity signal of the first test beam and the phase of the intensity signal of the first reference beam; and Determining a refractive index, an extinction coefficient and a thickness of the first test layer in a first region along the first test layer based on the difference between the phase of the first intensity signal of the first test beam and the phase of the intensity signal of the first reference beam, and determining the refractive index, the extinction coefficient and the thickness of the first test layer in a second region spaced apart from the first region along the first test layer based on the difference between the phase of the second intensity signal of the first test beam and the phase of the intensity signal of the first reference beam. [10] Method according to claim 9, wherein the second part of the first source beam is stretched and collimated with the beam stretcher such that a surface of the first test layer is covered by the stretched beam. [11] The method of claim 9 or 10, further comprising: Setting the first angle of incidence by rotating the first test layer around an axis; and Rotating the second analyzer and the second light sensor around the axis in response to the rotation of the first test layer around the axis. [12] Method according to any one of claims 9 to 11, further comprising: Reflecting, with a mirror, the second part of the first source beam to the beam extender and the first test layer; and Adjusting the first angle of incidence by rotating the first test layer, the mirror and the beam expander around an axis. [13] Method according to any one of claims 9 to 12, further comprising: Reflecting, with a mirror, the second part of the first source beam to the beam extender and the first test layer; Adjusting the initial angle of incidence by rotating the mirror and the beam expander around an axis; and Rotating the second analyzer and the second light sensor around the axis in response to the rotation of the mirror and the beam expander around the axis. [14] Method according to any one of claims 9 to 13, further comprising: Reflecting, with a beam splitter, the first part of the first source beam before polarizing the first part of the first source beam; and Passing through, with the beam splitter, the second part of the first source beam before stretching the second part of the first source beam. [15] Method according to any one of claims 9 to 14, wherein the first source beam of heterodyne light is generated by generating a precursor beam with s-polarized light and p-polarized light and modulating a phase difference between the s-polarized light and the p-polarized light of the precursor beam according to a modulation frequency. [16] Device with: a heterodyne light source arranged in such a way that it generates a first source beam of heterodyne light to a first test layer; a beam splitter that is arranged between the heterodyne light source and the first test layer and is configured to reflect a first part of the first source beam and to transmit a second part of the first source beam; a first analyzer which is set up to polarize the first part of the first source beam, thereby creating a first reference beam; a first light sensor configured to measure the intensity of the first reference beam, wherein the first analyzer is arranged between the beam splitter and the first light sensor; a beam expander positioned between the beam splitter and the first test layer, configured to expand and collimate the second part of the first source beam, thereby producing an expanded beam; a second analyzer configured to stretch a portion of the stretched beam reflected from the first test layer, thereby creating a first test beam; a second light sensor containing a first pixel and a second pixel configured to measure the intensity of the first test beam, the second analyzer being positioned between the first test layer and the second light sensor; and a characterization circuit connected to the first light sensor and the second light sensor, configured to determine a difference between the phase of an intensity signal of the first test beam and the phase of an intensity signal of the first reference beam, and to determine a refractive index, an extinction coefficient, and a thickness of the first test layer based on the difference between the phase of the intensity signal of the first test beam and the phase of the intensity signal of the first reference beam. [17] Device according to claim 16, further comprising: a first actuator configured to rotate the first test layer around an axis in order to set an angle of incidence at which the stretched beam of rays strikes the first test layer; and a second actuator, which is set up to rotate the second analyzer and the second light sensor around the axis. [18] Device according to claim 16 or 17, further comprising: a mirror that is arranged between the beam splitter and the beam expander and is configured to reflect the second part of the first source beam to the beam expander and the first test layer; a first actuator configured to rotate the first test layer around an axis; and a second actuator, which is set up to rotate the mirror and the beam expander around the axis in order to set an angle of incidence at which the expanded beam of light hits the first test layer. [19] Device according to any one of claims 16 to 18, further comprising: a mirror that is arranged between the beam splitter and the beam expander and is configured to reflect the second part of the first source beam to the beam expander and the first test layer; a first actuator configured to rotate the mirror and beam stretcher around an axis to set an angle of incidence at which the stretched beam of light strikes the first test layer; and a second actuator, which is set up to rotate the second analyzer and the second light sensor around the axis. [20] Device according to any one of claims 16 to 19, wherein the heterodyne light source has a laser light source which is configured to produce a laser beam with s-polarized light and p-polarized light, and the heterodyne light source further includes a modulator that is configured to modulate a phase difference between the s-polarized light and the p-polarized light of the laser beam.

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