Tunable wavelength optical fiber light source and overlay measurement device equipped with the same

Abstract

The present invention relates to an optical fiber light source and an overlay measurement device including the same, and more particularly to a tunable optical fiber light source capable of changing the wavelength of light output and an overlay measurement device including the same. The present invention provides a tunable optical fiber light source including: a broadband light source configured to emit light; a light source housing forming an internal space for accommodating the broadband light source and having a first window and a second window through which the light emitted from the broadband light source passes; a first variable filter disposed in an optical path of a first illumination source exiting from the first window and configured to adjust a wavelength band of the first illumination source; a second variable filter disposed in an optical path of a second illumination source exiting from the second window and configured to adjust a wavelength band of the second illumination source; and an optical fiber combiner including first and second input ports into which the first illumination source transmitted through the first variable filter and the second illumination source transmitted through the second variable filter are input, respectively, and an output port from which the first illumination source and the second illumination source are mixed and output.

Description

[Technical Field]

[0001] The present invention relates to an optical fiber light source and an overlay measurement device equipped with the same, and more particularly to a wavelength-tunable optical fiber light source capable of changing the wavelength of light output, and an overlay measurement device equipped with the same. [Background technology]

[0002] Advances in technology require a decrease in the size of semiconductor devices and an increase in the density of integrated circuits. To meet these requirements, various critical conditions must be met. Overlay tolerance is one of these critical conditions.

[0003] Semiconductor devices are manufactured through numerous manufacturing processes. To form an integrated circuit on a wafer, many manufacturing processes must be performed to ensure that desired circuit structures and elements are formed in specific locations in a sequential manner. The manufacturing process sequentially creates patterned layers on the wafer. This repeated stacking process creates electrically active patterns within the integrated circuit. If the individual structures are not aligned within the tolerances allowed by the production process, interference between the electrically active patterns can occur, potentially affecting the performance and reliability of the manufactured circuit. Overlay metrology tools are used to measure and verify alignment errors between these layers.

[0004] Common overlay measurement methods are used to measure and verify whether the alignment between two layers is within tolerance. One method involves forming structures called overlay marks at specific locations on a substrate and measuring the overlay by photographing these structures with optical image acquisition equipment. The measurement structures are designed to measure the overlay in at least one of the X and Y directions for each layer. Each structure is designed symmetrically, and the center value between structures arranged in the symmetrical direction is calculated and used as the representative value for that layer. The relative difference between the representative values ​​for each layer is then calculated to derive the overlay error.

[0005] To measure the overlay of two layers, as shown in Figures 1 and 2, a rectangular outer box 1 and a rectangular inner box 2 smaller than the outer box 1 are formed as two continuous layers. Then, as shown in Figure 3, the focus is adjusted on the outer box 1, and a waveform showing the change in intensity at each position is acquired to obtain the center value C1 of the outer box 1. Then, as shown in Figure 4, the focus is adjusted on the inner box 2, and a waveform showing the change in intensity at each position is acquired to obtain the center value C2 of the inner box 2, thereby measuring the overlay error between the two layers.

[0006] However, this conventional method has the problem that if there is a large difference in height between the layer on which the outer box 1 is formed and the layer on which the inner box 2 is formed, when focusing on one of the outer box 1 and the inner box 2, the other will not be in focus, and the out-of-focus image will be displayed blurry.

[0007] Furthermore, there is a problem in that the waveforms or images of the outer box 1 and the inner box 2 are obtained using the same beam without taking into consideration that the outer box 1 and the inner box 2 are formed on different layers using different materials and that the outer box 1 is covered by the layer on which the inner box 2 is formed.

[0008] With the development of semiconductor process technology, there is now a need to accurately and quickly measure overlay errors between layers with large height differences and different optical properties, and there is an increasing demand to solve these problems. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-2003-0054781 [Patent Document 2] Korean Patent No. 10-0689709 [Patent Document 3] Korean Patent No. 10-1564312 [Patent Document 4] Korean Patent Publication No. 10-2018-0042649 [Patent Document 5] Korean Patent Publication No. 10-2018-0045026 [Patent Document 6] Japanese Patent Publication No. 2005-519460 [Patent Document 7] Korean Patent No. 10-2120551 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to solve the above-mentioned problems by providing a tunable optical fiber light source capable of generating a beam suitable for illuminating an overlay mark including an overlay structure formed of materials with different optical properties in different layers.

[0011] Another object of the present invention is to provide a new overlay measurement apparatus that includes the above-mentioned light source and is capable of accurately and quickly measuring overlay errors between layers having different optical properties. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention provides a tunable optical fiber light source including: a broadband light source configured to emit light; a light source housing having an internal space to accommodate the broadband light source, a first window through which light emitted from the broadband light source passes to form a first illumination, and a second window through which light emitted from the broadband light source passes to form a second illumination; a first variable filter disposed in an optical path of the first illumination emitted from the first window and configured to adjust a wavelength band of the first illumination; a second variable filter disposed in an optical path of the second illumination emitted from the second window and configured to adjust a wavelength band of the second illumination; and an optical fiber combiner having first and second input ports into which the first illumination transmitted through the first variable filter and the second illumination transmitted through the second variable filter are input, respectively, and an output port from which the first illumination and the second illumination are mixed and output.

[0013] The present invention also provides a tunable optical fiber light source, further including: a first lens assembly configured to focus the first illumination transmitted through the first window toward the first variable filter; and a second lens assembly configured to focus the second illumination transmitted through the second window toward the second variable filter.

[0014] Also, the present invention provides a wavelength tunable optical fiber light source, wherein the first lens assembly includes a collimating lens and a focusing lens through which the light transmitted through the first window is transmitted in turn, and the second lens assembly includes a collimating lens and a focusing lens through which the light transmitted through the second window is transmitted in turn.

[0015] Also provided is a tunable optical fiber light source, further including: a third lens assembly configured to focus the first illumination transmitted through the first variable filter toward the first input port; and a fourth lens assembly configured to focus the second illumination transmitted through the second variable filter toward the second input port.

[0016] The third lens assembly includes a collimating lens and a focusing lens through which the light transmitted through the first variable filter is transmitted in turn, and the fourth lens assembly includes a collimating lens and a focusing lens through which the light transmitted through the second variable filter is transmitted in turn, in a tunable optical fiber light source.

[0017] Also provided is a wavelength tunable optical fiber light source in which the wavelength band of the first illumination and the wavelength band of the second illumination are different from each other.

[0018] Also provided is a wavelength tunable optical fiber light source, in which the wavelength band of the first illumination and the wavelength band of the second illumination are the same.

[0019] The present invention also provides an overlay measurement apparatus for measuring an inter-layer overlay error of a sample having overlay marks formed thereon, the overlay marks including a first overlay mark and a second overlay mark formed on different layers, the overlay measurement apparatus including: an illumination optical system configured to illuminate the overlay mark on the sample; a main beam splitter configured to split light reflected from the overlay mark into a first beam and a second beam; a first detector configured to receive the first beam and generate a first overlay mark image focused on the first overlay mark; a second detector configured to receive the second beam and generate a second overlay mark image focused on the second overlay mark; a first imaging optical system configured to image the first beam onto the first detector; and a second imaging optical system configured to image the second beam onto the second detector, wherein the illumination optical system includes the above-mentioned tunable optical fiber light source.

[0020] The present invention also provides an overlay measurement device that further includes a height difference detection optical system configured to detect a height difference Δh between the first overlay mark and the second overlay mark, wherein the second imaging optical system is a telecentric imaging optical system that includes an optical path adjustment unit configured to adjust the length of the optical path of the second beam based on the height difference, and is disposed between the main beam splitter and the second detector and configured to image the second beam onto the second detector.

[0021] The optical path adjusting unit includes at least one mirror disposed between the main beam splitter and the second detector and reflecting the second beam toward the second detector, a mirror stage configured to linearly move the at least one mirror to adjust the length of the optical path of the second beam, and a controller configured to control the mirror stage based on the height difference.

[0022] The controller controls the mirror stage so that the optical path of the second beam is extended in proportion to the product of the height difference and the magnification of the second overlay mark image, and the extended optical path of the second beam is longer than the optical path of the first beam.

[0023] The present invention also provides an overlay measurement apparatus, wherein the sample is a semiconductor wafer.

[0024] Also provided is an overlay measurement apparatus, wherein the first variable filter is configured to adjust a wavelength band of the first illumination to detect the first overlay mark on a first one of the other layers using the first detector.

[0025] Also provided is an overlay measurement apparatus, wherein the second variable filter is configured to adjust a wavelength band of the second illumination to detect the second overlay mark on a second one of the other layers using the second detector.

[0026] The present invention also provides an overlay measurement apparatus, in which the wavelength band of the first illumination and the wavelength band of the second illumination are different.

[0027] The present invention also provides an overlay measurement apparatus, wherein the wavelength band of the first illumination and the wavelength band of the second illumination are the same.

[0028] Also provided is an overlay measurement apparatus further including a detector controller configured to synchronize the first detector and the second detector.

[0029] Also provided is an overlay measurement apparatus, wherein the detector controller generates a software synchronization signal and transmits the synchronization signal to the first detector and the second detector.

[0030] Also provided is an overlay measurement apparatus further including a focus actuator for adjusting the position of the second detector.

[0031] The present invention also provides an overlay measurement apparatus, wherein the second imaging optical system includes a zoom lens located between the main beam splitter and the focus actuator, and the position-adjustable second detector and the zoom lens are configured to image the second beam onto the second detector. [Effects of the Invention]

[0032] A tunable fiber optic light source according to the present invention can produce illumination suitable for illuminating an overlay mark that includes overlay structures formed from materials with different optical properties in different layers. [Brief explanation of the drawings]

[0033] [Figure 1] FIG. 2 is a plan view of an overlay mark. [Figure 2] FIG. 2 is a side view of the overlay mark shown in FIG. 1. [Figure 3] 2 is a diagram showing waveforms of changes in signal intensity at different positions acquired with the focus on the outer box of the overlay mark shown in FIG. 1; [Figure 4] 2 is a diagram showing waveforms of changes in signal intensity at different positions acquired with the focus on the inner box of the overlay mark shown in FIG. 1. FIG. [Figure 5] 1 is a conceptual diagram of an overlay measurement apparatus according to an embodiment of the present invention. [Figure 6] FIG. 6 is a schematic diagram of the tunable optical fiber light source shown in FIG. 5. [Figure 7] 7 is a diagram showing the intensity of the first illumination that has passed through the first variable filter shown in FIG. 6 according to wavelength. [Figure 8] 7 is a diagram showing the intensity of the second illumination that has passed through the second variable filter shown in FIG. 6 according to wavelength. [Figure 9] FIG. 7 is a diagram showing the intensity of illumination passing through the fiber optic combiner shown in FIG. 6 according to wavelength. [Figure 10]10A and 10B are diagrams illustrating a method for irradiating a first overlay mark and a second overlay mark formed on a sample with illumination. [Figure 11] FIG. 6 shows a first overlay mark image acquired by the first detector shown in FIG. 5. [Figure 12] FIG. 6 shows a second overlay mark image acquired with the second detector shown in FIG. 5. [Figure 13] FIG. 10 shows an image obtained by combining a first overlay mark image and a second overlay mark image. [Figure 14] FIG. 10 is a conceptual diagram of an overlay measurement apparatus according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the embodiment of the present invention can be modified into various other forms, and the scope of the present invention should not be interpreted as being limited to the embodiment described below. The embodiment of the present invention is provided to more completely explain the present invention to those skilled in the art. Therefore, the shapes of elements in the drawings are exaggerated to emphasize a clearer description, and elements represented by the same reference numerals in the drawings refer to the same elements.

[0035] 5 is a conceptual diagram of an overlay measurement apparatus according to an embodiment of the present invention, which measures the error between a first overlay mark OM1 and a second overlay mark OM2 formed on different layers of a sample such as a semiconductor wafer, thereby measuring the overlay error between the different layers.

[0036] 10, the second overlay mark OM2 may be an overlay mark formed on a previous layer, and the first overlay mark OM1 may be an overlay mark formed on a current layer. The overlay marks are formed in the scribe lanes simultaneously with the formation of layers for forming semiconductor devices in the die region of the semiconductor wafer. For example, the second overlay mark OM2 may be formed together with an insulating film pattern, and the first overlay mark OM1 may be formed together with a photoresist pattern formed on the insulating film pattern.

[0037] In this case, the first overlay mark OM1 is exposed to the outside, but the second overlay mark OM2 is covered with a photoresist layer and is made of an oxide whose optical properties are different from those of the first overlay mark OM1, which is made of a photoresist material.The first overlay mark OM1 and the second overlay mark OM2 also have different heights.

[0038] In the present invention, a first overlay mark image I1 can be acquired by focusing a beam on the first overlay mark OM1 and using a beam suited to the optical properties of the material comprising the first overlay mark OM1. Also, a second overlay mark image I2 can be acquired by focusing a beam on the second overlay mark OM2 and using a beam suited to the optical properties of the material comprising the second overlay mark OM2. These first and second overlay mark images I1 and I2 can then be used to measure overlay errors accurately and quickly.

[0039] The overlay mark may be of various types currently in use, such as a box-in-box (BIB, see Figure 1), an AIM (advanced imaging metrology) overlay mark, etc. The following description will be centered on a box-in-box type overlay mark, which has a simple structure.

[0040] As shown in FIG. 5, an overlay measurement apparatus according to one embodiment of the present invention includes a height difference detection optical system 10, an illumination optical system 20, a main beam splitter 30, a first detector 40, a second detector 50, a first imaging optical system 60, and a second imaging optical system 70.

[0041] The height difference detection optical system 10 serves to measure the height difference Δh between the first overlay mark OM1 and the second overlay mark OM2. The height difference detection optical system 10 can be configured using various optical elements. The height difference detection optical system 10 can also be used as an autofocus optical system.

[0042] 5, the height difference detection optical system 10 may include a light source 11, a collimating lens 13 that collimates the beam from the light source 11, a beam splitter 15, and an image sensor 19. The height difference detection optical system 10 may further include a hot mirror 17, a beam splitter 31, and an objective lens 32 that are used in common with the first imaging optical system 60, the illumination optical system 40, and the second imaging optical system 70.

[0043] A laser diode or a light emitting diode can be used as the light source 11. The light source 11 can generate light in the infrared wavelength band.

[0044] Light generated by the light source 11 passes through the collimator 13 and the beam splitter 15. When a laser is used as the light source 11, a polarizing beam splitter can be used as the beam splitter 15. This is because it is possible to minimize the loss of light intensity during the reflection and transmission processes.

[0045] The hot mirror 17 serves to reflect light in the infrared wavelength band. The light reflected by the hot mirror 17 passes through a beam splitter 31 and enters an objective lens 32.

[0046] The objective lens 32 focuses light onto a measurement position on the surface of the sample S and collects the reflected light reflected at the measurement position on the surface of the sample S. The reflected light collected by the objective lens 32 passes through the beam splitter 31 again and is reflected by the hot mirror 17. The reflected light reflected by the hot mirror 17 is reflected from the beam splitter 15 to the image sensor 19 and then focused on the image sensor 19 by the focusing lens 18. Light in the infrared wavelength band does not pass through the hot mirror 17, so the light used for measuring the height difference does not enter the first detector 40.

[0047] The image sensor 19 receives light reflected from the sample S. The image sensor 19 may be a CCD sensor or a CMOS sensor. By analyzing the contrast of the image from the image sensor 19, it is possible to determine whether the image is in focus. Therefore, by analyzing the optical signal from the image sensor 19 according to the distance between the objective lens 32 and the sample S, it is possible to determine the position of the objective lens 32 when it is in focus on the first overlay mark OM1 and the position of the objective lens 32 when it is in focus on the second overlay mark OM2. Then, by comparing these positions, it is possible to determine the height difference Δh between the first overlay mark OM1 and the second overlay mark OM2.

[0048] The illumination optical system 20 serves to illuminate the overlay mark. The illumination optical system 20 can be configured using various optical elements. For example, as shown in FIG. 5, the illumination optical system 20 can include a tunable optical fiber light source 100 and a relay lens 28. A beam splitter 31 and an objective lens 32 can also be used as part of the illumination optical system 20.

[0049] Figure 6 is a schematic diagram of one embodiment of the tunable optical fiber light source shown in Figure 5. As shown in Figure 6, the tunable optical fiber light source 100 includes a broadband light source 110, a light source housing 120, a first tunable filter 130, a second tunable filter 140, an optical fiber combiner 150, a first lens assembly 160, a second lens assembly, a third lens assembly 180, and a fourth lens assembly 190.

[0050] The broadband light source 110 generates light in a wide wavelength band. The broadband light source 110 emits light in all directions. The broadband light source 110 can be an arc lamp, a discharge lamp, an electrodeless lamp, a halogen lamp, a xenon lamp, or the like.

[0051] The light source housing 120 includes an internal space for accommodating the broadband light source 110. The light source housing 120 includes a first window 121 and a second window 123 through which light emitted from the broadband light source 110 passes. The light emitted from the broadband light source 110 and passing through the first window 121 forms a first illumination. The light emitted from the broadband light source 110 and passing through the second window 123 forms a second illumination. A first cover glass 125 and a second cover glass 127 may be provided on the first window 121 and the second window 123, respectively. The first cover glass 125 and the second cover glass 127 serve to protect the broadband light source 110 from external damage and may also serve to block light in unused wavelength bands.

[0052] The first variable filter 130 serves to adjust the center wavelength and bandwidth of the first illumination transmitted through the first window 121 so that it is suitable for detecting the first overlay mark OM1 formed on the current layer. For example, the center wavelength can be adjusted to increase the reflectivity of the material that forms the first overlay mark OM1. The first variable filter 130 may include, for example, multiple circular or linear variable filters 131, 133 arranged side by side. Alternatively, the first variable filter 130 may include a single circular or linear variable filter.

[0053] Fig. 7 is a diagram illustrating the intensity of the first illumination light according to wavelength after passing through the first variable filter 130 shown in Fig. 6. As shown in Fig. 7, the first illumination light passing through the first variable filter 130 has a shorter central wavelength and a narrower bandwidth. The first illumination light passing through the first variable filter 130 may be illumination light in the visible light region.

[0054] The second variable filter 140 serves to adjust the center wavelength and bandwidth of the second illumination transmitted through the second window 123 to suit detection of the second overlay mark OM2 formed on the previous layer. For example, the center wavelength can be adjusted to have high transmittance for the material forming the first overlay mark OM1 and high reflectance for the material forming the second overlay mark OM2. The second variable filter 140 may include, for example, multiple circular or linear variable filters 141, 143 arranged side by side. Alternatively, the second variable filter 140 may include a single circular or linear variable filter.

[0055] Fig. 8 is a diagram illustrating the intensity of the second illumination light passing through the second variable filter 140 according to wavelength. As shown in Fig. 8, the second illumination light passing through the second variable filter 140 has a longer central wavelength and a smaller bandwidth. The second illumination light passing through the second variable filter 140 may be illumination light in the near-infrared (NIR) region.

[0056] The fiber optic combiner 150 combines the first and second illuminations. The fiber optic combiner has the advantage of having less loss than other types of beam combiners that use beam splitters or mirrors. By using the fiber optic combiner, it is possible to obtain illumination with a high light intensity of about 60%.

[0057] The optical fiber combiner 150 has a first input port 151 and a second input port 153 into which the first illumination light transmitted through the first variable filter 130 and the second illumination light transmitted through the second variable filter 140 are respectively input. The optical fiber combiner 150 also has an output port 155 from which the first illumination light and the second illumination light are mixed and output. The first illumination light that enters the first input port 151 is guided by a first input fiber 152. The second illumination light that enters the second input port 153 is guided by a second input fiber 154. The first illumination light and the second illumination light are combined at a position where the first input fiber 152 and the second input fiber 154 meet. The first illumination light and the second illumination light are then guided by an output fiber 156 and output via the output port 155.

[0058] Figure 9 is a diagram illustrating the intensity by wavelength of the illumination that has passed through the fiber optic combiner shown in Figure 6. As shown in Figure 9, the illumination that has passed through the fiber optic combiner 150 includes both the wavelength band of the first illumination and the wavelength band of the second illumination.

[0059] If it is necessary to ensure a sufficient amount of light, unlike the example shown in Figure 9, the wavelength band of the first illumination and the wavelength band of the second illumination may be the same, in which case approximately twice the amount of light can be obtained.

[0060] The first lens assembly 160 serves to collect the first illumination transmitted through the first window 121 toward the first variable filter 130. The first lens assembly 160 may include a collimating lens 161 and a focusing lens 163 through which the light transmitted through the first window 121 is transmitted in order.

[0061] The second lens assembly 170 serves to collect the second illumination transmitted through the second window 123 toward the second variable filter 140. The second lens assembly 170 may include a collimating lens 171 and a focusing lens 173 through which the light transmitted through the second window 123 is transmitted in order.

[0062] The third lens assembly 180 serves to collect the first illumination transmitted through the first variable filter 130 toward the first input port 151. The third lens assembly 180 may include a collimating lens 181 and a focusing lens 183, through which the light transmitted through the first variable filter 130 passes in turn.

[0063] The fourth lens assembly 190 serves to collect the second illumination transmitted through the second variable filter 140 toward the second input port 153. The fourth lens assembly 190 may include a collimating lens 191 and a focusing lens 193, through which the light transmitted through the second variable filter 140 passes in turn.

[0064] The illumination emitted from the wavelength-tunable optical fiber light source 100 passes through a relay lens 28 and is reflected by a beam splitter 31 toward an objective lens 32 .

[0065] The objective lens 32 focuses the illumination reflected by the beam splitter 31 onto the measurement position of the sample S and collects the reflected beam at the measurement position. The objective lens 32 is mounted on a lens focus actuator 33 for adjusting the distance between the objective lens 32 and the sample S.

[0066] As shown in FIG. 10, a sample S is illuminated together with a first illumination (solid line) and a second illumination (dashed line) via an illumination optical system 20.

[0067] The main beam splitter 30 serves to split the beam collected by the objective lens 32 into two beams. The main beam splitter 30 may be a beam splitter that splits the incident light into two spectrally distinct output beams. For example, the main beam splitter 30 may include a tube beam splitter and a dichroic filter. A dichroic filter is a filter that transmits beams of specific wavelengths. The beam collected by the objective lens 32 passes through the beam splitter 31 and the hot mirror 17, and is then split into two beams by the main beam splitter 30. That is, the beam is split into a first beam for detecting the first overlay mark OM1 and a second beam for detecting the second overlay mark OM2. The first beam may have substantially the same wavelength band as the first illumination, and the second beam may have the same wavelength band as the second illumination.

[0068] As shown in Figures 7 and 8, the first illumination suitable for detecting the first overlay mark OM1 and the second illumination suitable for detecting the second overlay mark OM2 have different central wavelengths and narrow bandwidths, so they can be easily separated into two beams using a dichroic filter.

[0069] The first detector 40 receives the first beam, which is one of the beams split by the main beam splitter 30, and serves to generate a first overlay mark image I1.

[0070] Figure 11 is a diagram showing the first overlay mark image I1 acquired by the first detector shown in Figure 5. As shown in Figure 11, the first overlay mark image I1 acquired by the first detector 40 shows the first overlay mark OM1 clearly, and the second overlay mark OM2 blurred, because the focus is based on the first overlay mark OM1.

[0071] The second detector 50 receives the second beam, which is the other one of the beams split by the main beam splitter 30, and generates a second overlay mark image I2.

[0072] The second detector 50 may be synchronized with the first detector 40 to minimize errors that may occur due to vibration during the overlay measurement process. The synchronization of the first detector 40 and the second detector 50 may be performed, for example, by generating a software synchronization signal in the detector controller 82 and transmitting it to the detectors 40 and 50. In this case, to prevent signal delay, the generated synchronization signal may be transmitted to the detectors 40 and 50 via an optical cable. The synchronization signal may also be generated by a separate external trigger source. The detector controller 82 may include at least one processor and at least one memory in which commands executable by the at least one processor are stored.

[0073] Figure 12 is a diagram showing the second overlay mark image I2 acquired by the second detector shown in Figure 5. As shown in Figure 12, the second overlay mark image I2 acquired by the second detector 50 shows the second overlay mark OM2 clearly, while the first overlay mark OM1 appears blurred. This is because the optical path of the second beam is adjusted by the second imaging optical system 70 so that the second overlay mark OM2 is focused.

[0074] By aligning and combining the image of FIG. 11 and the image of FIG. 12, an overlay mark image can be obtained in which both the first overlay mark OM1 and the second overlay mark OM2 are clearly displayed, as shown in FIG. 13.

[0075] The first imaging optics 60 serves to image the first beam onto the first detector 40 .

[0076] 5, the first imaging optics 60 can include a tube lens 65 and a first optical filter 68. The first imaging optics 60 also uses the objective lens 32, the beam splitter 31, the hot mirror 17, and the main beam splitter 30 of other optics.

[0077] Objective lens 32 collects light reflected from sample S. The light collected by objective lens 32 is split into a first beam and a second beam by main beam splitter 30. The first beam transmitted through main beam splitter 30 is focused onto first detector 40 by tube lens 65. At this time, the focus is adjusted based on first overlay mark OM1. Therefore, in first overlay mark image I1 generated by first detector 40, first overlay mark OM1 appears clearly, while second overlay mark OM2 appears relatively blurred.

[0078] The first optical filter 68 is disposed at the front end of the first detector 40 and serves to secondarily adjust the center wavelength and bandwidth of the first beam for acquiring the first overlay mark image I1. The first optical filter 68 may include multiple linear or rotary variable filters arranged side by side. Additionally, the first optical filter 68 may include a single linear or rotary variable filter. In some embodiments, the first optical filter 68 may be omitted.

[0079] The second imaging optical system 70 adjusts the length of the optical path of the second beam based on the height difference Δh between the first overlay mark OM1 and the second overlay mark OM2 to image the second beam on the second detector 50. It also adjusts the chief ray of the second beam to be perpendicularly incident on the second detector 50. The second imaging optical system 70 is preferably a telecentric imaging optical system.

[0080] The second imaging optical system 70 includes an optical path adjusting unit 75 , a telecentric lens 77 , and a second optical filter 78 .

[0081] The optical path adjusting unit 75 includes mirrors 71, 72, and 73, a mirror stage 74, and a controller 79. The controller 79 may include at least one processor and at least one memory that stores commands executable by the at least one processor. The mirrors 71, 72, and 73 serve to reflect the second beam reflected from the main beam splitter 30 to make it incident on the second detector 50. In this embodiment, the optical path adjusting unit 75 includes three mirrors 71, 72, and 73.

[0082] The mirror stage 74 can serve to simultaneously linearly move the two mirrors 71 and 72 located on the right side of the drawing. When these two mirrors 71 and 72 are moved to the right side of the drawing, the distance between the main beam splitter 30 and the mirror 71 and the distance between the mirrors 72 and 73 increase, lengthening the optical path.

[0083] The controller 79 adjusts the movement distance of the mirror stage 74 based on the height difference Δh. The controller 79 moves the mirror stage 74 based on the product of the height difference Δh and the magnification of the second overlay mark image I2 so that the overall optical path of the second beam is longer than the overall optical path of the first beam. The magnification of the second overlay mark image I2 refers to the ratio between the size of the actual second overlay mark OM2 and the size of the second overlay mark on the image. The magnification of the second overlay mark image I2 may be the same as the magnification of the first overlay mark image I1.

[0084] The telecentric lens 77 serves to make the distance of the optical path of the second beam and the magnification of the image independent. The telecentric lens 77 is a lens that allows the optical axis and the chief ray of the second beam to be considered parallel. The telecentric lens 77 can be disposed between the main beam splitter 30 and the optical path adjusting unit 75.

[0085] In the present invention, the use of telecentric lens 77 allows the magnification of second overlay mark image I2 to be fixed even if the optical path of the second beam changes. Therefore, focusing can be achieved without changing the magnification by adjusting the movement distance of mirror stage 74 in proportion to the measured height difference Δh. In second overlay mark image I2 generated by second detector 50, second overlay mark OM2 appears clear, while first overlay mark OM1 appears relatively blurred.

[0086] The second optical filter 78 is disposed at the front end of the second detector 50 and serves to secondarily adjust the center wavelength and bandwidth of the second beam for acquiring the second overlay mark image I2. The second optical filter 78 may include multiple linear or rotary variable filters arranged side by side. Alternatively, the second optical filter 78 may include a single linear or rotary variable filter. In this embodiment, the second optical filter 78 may be omitted.

[0087] Figure 14 is a conceptual diagram of an overlay measurement apparatus according to another embodiment of the present invention. The embodiment shown in Figure 14 differs from the embodiment shown in Figure 5 only in the configuration of the second imaging optics 270 and the second detector 250, and will therefore only be described in detail here.

[0088] The second detector 250 detects the beam reflected by the main beam splitter 30. The second detector 250 is installed on a focus actuator 251. Therefore, the distance between the main beam splitter 30 and the second detector 250 is adjustable.

[0089] Since the distance between the objective lens 32 and the sample S is adjusted so that the focal point is located on the first overlay mark OM1 with reference to the first imaging optical system 60, in order to obtain a clear image of the second overlay mark OM2, the distance between the second detector 250 and the main beam splitter 30 must be adjusted using the focus actuator 251 in accordance with the height difference between the first overlay mark OM1 and the second overlay mark OM2. The focus actuator 251 can be operated based on a signal from the height difference detection optical system 10.

[0090] In this embodiment, the second imaging optical system 270 includes a zoom lens 271. In addition, the objective lens 32, the beam splitter 31, the hot mirror 17, and the main beam splitter 30 are also used as parts of the second imaging optical system 270.

[0091] The zoom lens 271 is provided between the main beam splitter 30 and the focus actuator 251. The zoom lens 271 receives the position change value of the second detector 250 from the height difference detection optical system 10 or the focus actuator 251, and serves to match the magnification of the image of the second overlay mark OM2 with the image of the first overlay mark OM1 based on the received value.

[0092] Because the optical path distance between the second detector 250 and the main beam splitter 30 is adjusted to be different from the optical path distance between the first detector 40 and the main beam splitter 30 depending on the height difference between the first overlay mark OM1 and the second overlay mark OM2, the magnifications of the images acquired by the first detector 40 and the second detector 40 may differ from each other. To accurately measure the overlay error, the magnifications must match. In the embodiment shown in FIG. 5, a telecentric imaging optical system is used as the second imaging optical system 70, so a zoom lens may not be used.

[0093] The embodiments described above are merely preferred embodiments of the present invention, and the scope of the present invention is not limited to the described embodiments. Various modifications, variations, or substitutions may be made by those skilled in the art within the technical spirit and scope of the claims of the present invention, and it should be understood that these embodiments also fall within the scope of the present invention. [Explanation of symbols]

[0094] S Sample OM1 First Overlay Mark OM2 Second Overlay Mark 10 Height difference measurement optical system 20 Illumination optical system 30 Main beam splitter 40 First Detector 50, 250 Second detector 60 First imaging optical system 70, 270 Second imaging optical system 100 Tunable optical fiber light source 110 Broadband Light Source 120 Light source housing 130 First variable filter 140 Second variable filter 150 Optical Fiber Combiner 160 First Lens Assembly 170 Second Lens Assembly 180 Third Lens Assembly 190 4th lens assembly

Claims

1. a broadband light source configured to emit light; a light source housing having an interior space for accommodating the broadband light source, a first window through which light emitted from the broadband light source passes to form a first illumination, and a second window through which light emitted from the broadband light source passes to form a second illumination; a first variable filter disposed in an optical path of the first illumination exiting the first window and configured to adjust a wavelength band of the first illumination; a second variable filter disposed in the optical path of the second illumination exiting the second window and configured to adjust a wavelength band of the second illumination; a fiber optic combiner including a first input port and a second input port into which a first illumination transmitted through the first variable filter and a second illumination transmitted through the second variable filter are respectively input, and an output port from which the first illumination and the second illumination are mixed and output.

2. a first lens assembly configured to focus the first illumination transmitted through the first window toward the first variable filter; 10. The tunable fiber optic light source of claim 1, further comprising: a second lens assembly configured to focus the second illumination transmitted through the second window toward the second tunable filter.

3. the first lens assembly includes a collimating lens and a focusing lens through which the light transmitted through the first window is transmitted in sequence; 3. The tunable optical fiber light source according to claim 2, wherein the second lens assembly includes a collimating lens and a focusing lens through which the light transmitted through the second window is transmitted in turn.

4. a third lens assembly configured to focus the first illumination transmitted through the first variable filter toward the first input port; 10. The tunable fiber optic light source of claim 1, further comprising: a fourth lens assembly configured to focus the second illumination transmitted through the second tunable filter toward the second input port.

5. the third lens assembly includes a collimating lens and a focusing lens through which the light transmitted through the first variable filter is transmitted in order; 5. The tunable optical fiber light source according to claim 4, wherein the fourth lens assembly includes a collimating lens and a focusing lens through which the light transmitted through the second variable filter is transmitted in turn.

6. 2. The tunable optical fiber light source according to claim 1, wherein the wavelength band of the first illumination and the wavelength band of the second illumination are different from each other.

7. 2. The tunable optical fiber light source according to claim 1, wherein the wavelength band of the first illumination and the wavelength band of the second illumination are the same.

8. 1. An overlay measurement apparatus for measuring an inter-layer overlay error of a sample having overlay marks formed thereon, the overlay marks including a first overlay mark and a second overlay mark formed on different layers, the apparatus comprising: illumination optics configured to illuminate an overlay mark on the sample; a main beam splitter configured to split reflected light from the overlay mark into a first beam and a second beam; a first detector configured to receive the first beam and generate a first overlay mark image focused on the first overlay mark; a second detector configured to receive the second beam and generate a second overlay mark image focused on the second overlay mark; a first imaging optical system configured to image the first beam onto the first detector; second imaging optics configured to image the second beam onto the second detector; 10. An overlay measurement apparatus, wherein the illumination optical system includes the tunable optical fiber light source according to claim 1.

9. a height difference detection optical system configured to detect a height difference (Δh) between the first overlay mark and the second overlay mark; The second imaging optical system is 9. The overlay measurement apparatus of claim 8, wherein the overlay measurement apparatus is a telecentric imaging optical system including: an optical path adjusting unit configured to adjust the length of the optical path of the second beam based on the height difference; and a telecentric lens disposed between the main beam splitter and the second detector, the telecentric lens configured to image the second beam onto the second detector.

10. The optical path adjusting unit is at least one mirror disposed between the main beam splitter and the second detector, the mirror reflecting the second beam toward the second detector; a mirror stage configured to linearly move the at least one mirror to adjust the optical path length of the second beam; and a controller configured to control the mirror stage based on the height difference.

11. 11. The overlay measurement apparatus of claim 10, wherein the controller controls the mirror stage so that the optical path of the second beam is extended in proportion to the product of the height difference and the magnification of the second overlay mark image, and the extended optical path of the second beam is longer than the optical path of the first beam.

12. The overlay measurement apparatus of claim 8 , wherein the sample is a semiconductor wafer.

13. 9. The overlay measurement apparatus of claim 8, wherein the first variable filter is configured to adjust a wavelength band of the first illumination to detect the first overlay mark on a first one of the other layers with the first detector.

14. 9. The overlay measurement apparatus of claim 8, wherein the second variable filter is configured to adjust a wavelength band of the second illumination to detect the second overlay mark on a second one of the other layers with a second detector.

15. The overlay measurement apparatus of claim 8 , wherein the wavelength band of the first illumination and the wavelength band of the second illumination are different.

16. The overlay measurement apparatus of claim 8 , wherein the wavelength band of the first illumination and the wavelength band of the second illumination are the same.

17. The overlay measurement apparatus of claim 8 , further comprising a detector controller configured to synchronize the first detector and the second detector.

18. 18. The overlay measurement apparatus of claim 17, wherein the detector controller generates a software synchronization signal and transmits the synchronization signal to the first detector and the second detector.

19. The overlay measurement apparatus of claim 8 , further comprising a focus actuator for adjusting the position of the second detector.

20. the second imaging optical system includes a zoom lens located between the main beam splitter and the focus actuator; 20. The overlay measurement apparatus of claim 19, wherein the adjustable position second detector and the zoom lens are configured to image the second beam onto the second detector.

Images