Overlay measurement apparatus and method

Abstract

To provide an overlay measuring apparatus and method for accurately and quickly measuring an overlay error between layers having large height difference and different optical properties.SOLUTION: An overlay measuring apparatus comprises: a height difference detection optical system 10 that detects height difference (Δh) between a first overlay mark and a second overlay mark formed on layers different from each other; an illumination optical system 20 that illuminates the overlay mark; a main beam splitter 30 that separates reflected light from the overlay mark into a first beam and a second beam; a first detector 40 that receives the first beam and generates a first overlay mark image; a second detector 50 that receives the second beam and generates a second overlay mark image; an imaging optical system 60 that forms an image of the first beam on the first detector; an optical path control unit 75 that adjusts length of an optical path of the second beam based on height difference (Δh); and a telecentric imaging optical system 70 that forms an image of the second beam on the second detector.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an overlay measurement apparatus and method. [Background technology]

[0002] With the development of technology, the size of semiconductor devices is shrinking, and the density of integrated circuits needs to be increased. To meet these requirements, various conditions must be met, among which overlay tolerance is one of the important indicators.

[0003] Semiconductor devices are manufactured through a number of manufacturing processes. To form an integrated circuit on a wafer, many manufacturing processes must be performed so that desired circuit structures and elements are formed in specific locations in a sequential manner. The manufacturing processes sequentially create patterned layers on the wafer. Through these repeated stacking steps, electrically active patterns are created in the integrated circuit. If the structures are not aligned within an error range allowed by the production process, interference between the electrically active patterns may occur, which may cause problems in the performance and reliability of the manufactured circuit. Overlay measurement tools are used to measure and verify such alignment errors between layers.

[0004] A typical overlay measurement method measures and verifies whether the alignment between two layers is within a tolerance. One method is to form a structure called an overlay mark at a specific position on a substrate and measure the overlay by photographing the structure with an optical image acquisition device. The measurement structure is designed to measure the overlay in at least one of the X and Y directions for each layer. Each structure is designed as a symmetrical structure, and the center value between the structures arranged in the symmetrical direction is calculated and used as the representative value of the layer, and the relative difference between the representative values ​​of each layer is calculated to derive the overlay error.

[0005] When measuring the overlay of two layers, as shown in Figures 1 and 2, a rectangular main box (outer box) 1 and a rectangular secondary box (inner box) 2 smaller than the main box 1 are formed on two consecutive layers, and then, as shown in Figures 3 and 4, the focus is placed on the main box 1, a waveform showing the change in intensity at each position is obtained to obtain the center value C1 of the main box 1, and the focus is placed on the secondary box 2, a waveform showing the change in intensity at each position is obtained to obtain the center value C2 of the secondary box 2, thereby measuring the overlay error between the two layers.

[0006] However, such conventional methods have the problem that when there is a large difference in height between the layer on which the main scale 1 is formed and the layer on which the secondary scale 2 is formed, focusing on either the main scale 1 or the secondary scale 2 will result in the other being out of focus, resulting in a blurred display.

[0007] There is also a problem in that the waveforms or images of the main scale 1 and the secondary scale 2 are obtained using the same beam without taking into consideration that the main scale 1 and the secondary scale 2 are formed on different layers using different materials and that the main scale 1 is covered by the layer on which the secondary scale 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 having large height differences and different optical properties, and so there is an increasing demand to solve these problems. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 2003-0054781 [Patent Document 2] Korean Patent Registration No. 10-0689709 [Patent Document 3] Korean Patent Registration 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] JP2005-519460A [Patent Document 7] Korean Patent Registration No. 10-2120551 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention is made to improve the above-mentioned problems, and has an object to provide a new overlay measurement apparatus and method that can accurately and quickly measure the overlay error between layers that have a large height difference and different optical properties. [Means for solving the problem]

[0011] In order to achieve the above object, the present invention provides an overlay measurement device for measuring an inter-layer overlay error of a sample on which an overlay mark is formed, the inter-layer overlay error being measured, the inter-layer overlay error being measured on the sample on which an overlay mark is formed ... and a telecentric imaging optical system including a telecentric lens disposed between the main beam splitter and the second detector and configured to image the second beam on the first detector.

[0012] The present invention also provides an overlay measurement device, characterized in that the optical path adjustment 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 adjust the optical path length of the second beam by linearly moving the at least one mirror, and a controller configured to control the mirror stage based on the height difference.

[0013] The present invention also provides an overlay measurement apparatus, characterized in that 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.

[0014] The present invention also provides an overlay measurement apparatus, wherein the imaging optical system further includes a first optical filter arranged in front of the first detector and adjusting a central wavelength and bandwidth of the first beam for acquiring the first overlay mark image, and the telecentric imaging optical system further includes a second optical filter arranged in front of the second detector and adjusting a central wavelength and bandwidth of the second beam for acquiring the second overlay mark image.

[0015] The present invention also provides an overlay measurement apparatus, wherein the first optical filter and the second optical filter are linear or rotary variable filters.

[0016] Also provided is an overlay measurement apparatus, characterized in that the first detector and the second detector are synchronized so that the first overlay mark image and the second overlay mark image are generated simultaneously.

[0017] The present invention also provides an overlay measurement method for measuring an inter-layer overlay error of a sample on which an overlay mark is formed, the inter-layer overlay error being measured, the inter-layer overlay error being measured, the inter-layer overlay error being measured of the sample on which an overlay mark is formed ... adjusting an optical path length of the second beam based on the height difference Δh so that the second beam is focused on an overlay mark of the first overlay mark; imaging the second beam, which has passed through a telecentric lens and traveled through an optical path whose length has been adjusted, onto a second detector; generating a first overlay mark image focused on the first overlay mark by the first detector, and generating a second overlay mark image focused on the second overlay mark by the second detector.

[0018] Also, the present invention provides an overlay measurement method, characterized in 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 optical path length of the second beam is adjusted so that the optical path of the extended second beam is longer than the optical path of the first beam.

[0019] Also provided is an overlay measurement method, further comprising the steps of adjusting a central wavelength and a bandwidth of the first beam for acquiring the first overlay mark image, and adjusting a central wavelength and a bandwidth of the second beam for acquiring the second overlay mark image.

[0020] Also, there is provided an overlay measurement method, wherein a central wavelength of the first beam and a central wavelength of the second beam are different from each other.

[0021] Also provided is a method for overlay measurement, characterized in that the first detector and the second detector are synchronized such that the first overlay mark image and the second overlay mark image are generated simultaneously. Effect of the Invention

[0022] The overlay measurement apparatus and method according to the present invention have the advantage that they can accurately and quickly measure overlay errors between layers having large height differences and different optical properties. [Brief description of the drawings]

[0023] [Figure 1] FIG. 2 is a plan view of an overlay mark. [Diagram 2] FIG. 2 is a side view of the overlay mark shown in FIG. [Diagram 3] 2 shows a waveform of change in signal intensity according to position acquired with the focus on the main scale of the overlay mark shown in FIG. 1. [Figure 4] 2 shows a waveform of change in intensity of a signal with respect to a position acquired with the focus on the vernier of the overlay mark shown in FIG. 1. [Diagram 5] 1 is a conceptual diagram of an overlay measurement apparatus according to an embodiment of the present invention; [Figure 6] 6 is a diagram showing the intensity according to the wavelength of the first illumination passing through the first color filter shown in FIG. 5. FIG. [Figure 7] 6 is a diagram showing the intensity depending on the wavelength of the second illumination passed through the second color filter shown in FIG. 5. FIG. [Figure 8] FIG. 6 is a diagram showing the intensity of illumination passing through the beam combiner shown in FIG. 5 according to wavelength. [Figure 9] 13A to 13C are diagrams for explaining a method of irradiating a first overlay mark and a second overlay mark formed on a sample with illumination. [Figure 10] FIG. 6 shows a first overlay mark image captured by the first detector shown in FIG. 5. [Figure 11] FIG. 6 shows a second overlay mark image captured with a second detector shown in FIG. 5. [Figure 12] FIG. 2 shows an image obtained by combining a first overlay mark image with a second overlay mark image. [Figure 13] 4 is a flow chart of an overlay measurement method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] 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 in detail 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.

[0025] 5 is a conceptual diagram of an overlay measurement apparatus according to an embodiment of the present invention, which measures an 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 an overlay error between the different layers.

[0026] For example, as shown in Fig. 9, 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 a scribe lane at the same time as forming a layer for forming a semiconductor device in a die area of ​​a 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.

[0027] In such a case, the first overlay mark OM1 is exposed to the outside, while the second overlay mark OM2 is covered by a photoresist layer, which is made of an oxide having different optical properties from the first overlay mark OM1 made of a photoresist material, and the focal planes of the first overlay mark OM1 and the second overlay mark OM2 are different from each other.

[0028] The present invention obtains a first overlay mark image I1 using a beam that is focused on the first overlay mark OM1 and that matches the optical properties of the material that constitutes the first overlay mark OM1, and obtains a second overlay mark image I2 using a beam that is focused on the second overlay mark OM2 and that matches the optical properties of the material that constitutes the second overlay mark OM2.The first overlay mark image I2 and the second overlay mark image I2 can then be used to measure the overlay error accurately and quickly.

[0029] The overlay mark may be of various types currently used, such as a box-in-box (BIB, see FIG. 1) overlay mark, an advanced imaging metrology (AIM) overlay mark, etc. In the following, the description will be mainly based on a box-in-box type overlay mark, which has a simple structure.

[0030] 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, an imaging optical system 60, and a telecentric imaging optical system 70.

[0031] 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.

[0032] 5, the height difference detection optical system 10 may include a light source 11, a collimation lens 13 that collimates a beam from the light source 11, a beam splitter 15, and an image sensor 19. In addition, 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 imaging optical system 60, the illumination optical system 40, and the telecentric imaging optical system 70.

[0033] 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.

[0034] The 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 the reduction in the amount of light during the reflection and transmission processes can be minimized.

[0035] 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.

[0036] Objective lens 32 serves to focus light at a measurement position on the surface of sample S and collect the light reflected at the measurement position. The reflected light collected by objective lens 32 passes through beam splitter 31 again and is reflected by hot mirror 17. The reflected light reflected by hot mirror 17 is reflected from beam splitter 15 towards image sensor 19 and is then focused on image sensor 19 by focus lens 18. Light belonging to the infrared wavelength band does not pass through hot mirror 17, so the light used to measure the height difference does not enter first detector 40.

[0037] The image sensor 19 receives the reflected light 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 focus is correct or not. Therefore, by analyzing the optical signal from the detector 19 according to the distance between the objective lens 32 and the sample S, it is possible to find the position of the objective lens 32 when the first overlay mark OM1 is in focus and the position of the objective lens 32 when the second overlay mark OM2 is in focus. Then, by comparing these positions, it is possible to ascertain the height difference Δh between the first overlay mark OM1 and the second overlay mark OM2.

[0038] The illumination optical system 20 serves to illuminate the overlay mark. The illumination optical system can be configured using various optical elements. For example, as shown in FIG. 5, the illumination optical system 20 can include an illumination source 21, a beam splitter 22, a first color filter 24, a second color filter 25, mirrors 23 and 27, a beam combiner 26, and an objective lens 32.

[0039] The illumination source 21 generates light in a wide wavelength band, and may be a halogen lamp, a xenon lamp, a supercontinuum laser, a light-emitting diode, a laser induced lamp, or the like.

[0040] The beam splitter 22 plays a role in splitting the beam emitted from the illumination source 21 into two beams. That is, the beam splitter 22 splits the beam emitted from the illumination source 21 into two beams by transmitting a part of the beam and reflecting a part of the beam.

[0041] The first color filter 24 serves to adjust the central wavelength and bandwidth of the beam transmitted through the beam splitter 22 among the beams separated by the beam splitter 22 so as to be suitable for detecting the first overlay mark OM1 formed on the current layer. For example, the central wavelength can be adjusted so as to have a high reflectance with respect to the material constituting the first overlay mark OM1. The first color filter 24 may include, for example, a plurality of circular or linear variable filters arranged next to each other.

[0042] Figure 6 is a diagram showing the intensity according to wavelength of the first illumination passing through the first color filter shown in Figure 5. As shown in Figure 6, the first illumination passing through the first color filter 24 has a shorter central wavelength and a reduced bandwidth.

[0043] The second color filter 25 serves to adjust the central wavelength and bandwidth of the beam reflected by the beam splitter 22 among the beams split by the beam splitter 22 so as to be suitable for detecting the second overlay mark OM2 formed on the previous layer. For example, the central wavelength can be adjusted to have high transmittance for the material constituting the first overlay mark OM1 and high reflectance for the material constituting the overlay mark OM1. The second color filter 25 may include, for example, a plurality of circular or linear variable filters arranged next to each other.

[0044] The path of the beam reflected by the beam splitter 22 is changed by a mirror 23 disposed between the beam splitter 22 and a second color filter 25 so that the beam is directed toward a second color filter 25 .

[0045] Fig. 7 is a diagram showing the intensity according to the wavelength of the second illumination passing through the second color filter shown in Fig. 5. As shown in Fig. 7, the second illumination passing through the second color filter 25 has a longer central wavelength and a smaller bandwidth.

[0046] The beam combiner 26 serves to combine the first illumination with the second illumination, for example, the first illumination is transmitted through the beam combiner 26, the second illumination is redirected by a mirror 27 toward the beam combiner 26, and is then reflected by the beam combiner 26 and combined again with the first illumination transmitted through the beam combiner 26.

[0047] Figure 8 is a diagram illustrating the intensity by wavelength of the illumination passed through the beam combiner shown in Figure 5. As shown in Figure 8, the illumination passed through the beam combiner 26 includes both the wavelength band of the first illumination and the wavelength band of the second illumination.

[0048] The illumination combined by the beam combiner 26 passes through a relay lens 28 and is reflected by a beam splitter 31 toward an objective lens 32 .

[0049] The objective lens 32 serves to focus the illumination reflected by the beam splitter 31 onto a measurement position on the sample S and to collect 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.

[0050] As shown in FIG. 9, a first illumination (solid line) and a second illumination (dashed line) are irradiated together on a sample S.

[0051] 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 30 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 a beam of a specific wavelength. The beam collected by the objective lens 32 is split into two beams by the main beam splitter 30 after passing through the beam splitter 31 and the hot mirror 17. 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 be substantially the same wavelength band as the first illumination, and the second beam may be the same wavelength band as the second illumination.

[0052] As shown in Figures 6 and 7, the first illumination adapted to detect the first overlay mark OM1 and the second illumination adapted to detect 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.

[0053] The first detector 40 serves to receive the first beam, which is one of the beams split by the main beam splitter 30, and generate a first overlay mark image I1.

[0054] Fig. 10 is a diagram showing the first overlay mark image I1 acquired by the first detector shown in Fig. 5. As shown in Fig. 10, in the first overlay mark image I1 acquired by the first detector 40, the first overlay mark OM1 is displayed clearly and the second overlay mark OM2 is displayed blurred, because the focus is adjusted based on the first overlay mark OM1.

[0055] The second detector 50 serves to receive the second beam, which is another of the beams split by the main beam splitter 30, and generate a second overlay mark image I2.

[0056] The second detector 50 may be synchronized with the first detector 40 in order to minimize errors that may occur due to vibration during the overlay measurement process. The synchronization between 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 the signal to the detectors 40 and 50. In this case, in order 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 be generated by a separate external trigger source.

[0057] Figure 11 is a diagram showing the second overlay mark image I2 acquired by the second detector shown in Figure 5. As shown in Figure 11, in the second overlay mark image I2 acquired by the second detector 50, the second overlay mark OM2 is clearly displayed and the first overlay mark OM1 is blurred. This is because the optical path of the second beam has been adjusted by the telecentric imaging optics 70 so that the second overlay mark OM2 is clearly displayed.

[0058] By aligning the image of FIG. 10 with the image of FIG. 11, 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.

[0059] The imaging optics 60 serve to image the first beam onto the first detector 40 .

[0060] 5, the imaging optical system 60 can include a tube lens 65 and a first optical filter 68. The imaging optical system 60 also uses the objective lens 32, the beam splitter 31, the hot mirror 17, and the main beam splitter 30 of other optical systems.

[0061] The objective lens 32 collects light reflected from the sample S. The light collected by the objective lens 32 is split into a first beam and a second beam by the main beam splitter 30. The first beam transmitted through the main beam splitter 30 is focused on the first detector 40 by the tube lens 65. At this time, the focus is adjusted based on the first overlay mark. Therefore, in the first overlay mark image I1 generated by the first detector 40, the first overlay mark OM1 appears clear, and the second overlay mark OM2 appears relatively blurred.

[0062] The first optical filter 68 is disposed before the first detector 40 and serves to secondarily adjust the central wavelength and bandwidth of the first beam for acquiring the first overlay mark image I1. The first optical filter 68 can be a linear variable filter or a rotary variable filter. In some embodiments, the first optical filter 68 may be omitted.

[0063] The telecentric imaging optical system 70 functions to adjust the optical path length 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 onto the second detector 50. It also functions to make the chief ray of the second beam perpendicularly incident on the second detector 50.

[0064] The telecentric imaging optical system 70 includes an optical path adjustment unit 75 , a telecentric lens 77 , and a second optical filter 78 .

[0065] The optical path adjusting unit 75 includes mirrors 71, 72, and 73, a mirror stage 74, and a controller 79. 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.

[0066] In some embodiments, the mirror stage 74 can serve to simultaneously linearly move two mirrors 71, 72 located on the right side of the drawing. When these two mirrors 71, 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, 73 increase, thereby lengthening the optical path.

[0067] The controller 79 serves to adjust 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 between the total optical path of the second beam and the total optical path of the first beam and the magnification of the second overlay mark image I2. The magnification of the second overlay mark image I2 means the ratio between the actual size of the second overlay mark OM2 and the size of the second overlay mark on the image.

[0068] In some embodiments, the magnification of the second overlay mark image I2 may be the same as the magnification of the first overlay mark image I1.

[0069] The telecentric lens 77 plays a role in making the distance of the optical path of the second beam and the magnification of the image independent. The telecentric lens 77 is a lens in which the optical axis and the chief ray of the second beam are considered to be parallel. The telecentric lens 77 can be disposed between the main beam splitter 30 and the second detector 50. For example, the telecentric lens 77 can be disposed between the main beam splitter 30 and the optical path adjustment unit 75.

[0070] Since the telecentric lens 77 is used, the magnification of the second overlay mark image I2 can be fixed even if the optical path of the second beam changes. Therefore, the focus can be adjusted without changing the magnification by adjusting the movement distance of the mirror stage 74 in proportion to the measured height difference Δh. In the second overlay mark image I2 generated by the second detector 50, the second overlay mark OM2 appears clear, and the first overlay mark OM1 appears relatively blurred.

[0071] The second optical filter 78 is disposed before the second detector 50 and serves to secondarily adjust the central wavelength and bandwidth of the second beam for acquiring the second overlay mark image I2. The second optical filter 78 can be a linear variable filter or a rotary variable filter. In some embodiments, the second optical filter 78 may be omitted.

[0072] An overlay measurement method using the above-described overlay measurement device will be described below.

[0073] As shown in FIG. 13, the overlay measurement method includes the steps of detecting a height difference Δh between a first overlay mark and a second overlay mark (S1), illuminating the overlay mark on a sample (S2), splitting the reflected light from the overlay mark into two beams (S3), imaging the first beam onto a first detector (S4), adjusting the optical path length of the second beam (S5), imaging the second beam that has passed through a telecentric lens and traveled through an optical path with the adjusted length onto a second detector (S6), and generating a first overlay mark image I1 on the first detector and a second overlay mark image I2 on the second detector (S7).

[0074] In the step (S1) of detecting the height difference Δh between the first overlay mark and the second overlay mark, the height difference Δh between the first overlay mark OM1 and the second overlay mark OM2 is detected using a height difference detection optical system such as an autofocus device using a contrast detection method or a phase difference detection method.

[0075] Next, the illumination optical system is used to illuminate the overlay mark on the sample (S2).

[0076] As shown in FIG. 9, the illumination may include a wavelength band adapted to obtain a first overlay mark image I1 and a wavelength band adapted to obtain a second overlay mark image I2.

[0077] The reflected light from the overlay mark is then split (S3) into two beams, the first beam being a beam of a wavelength range adapted to image the first overlay mark and the second beam being a beam of a wavelength range adapted to image the second overlay mark.

[0078] Next, the first beam is imaged onto a first detector (S4).

[0079] In this step, a first beam of a wavelength band adapted for acquiring an image of the first overlay mark OM1 is imaged onto a first detector 40.

[0080] Next, the optical path length of the second beam is adjusted (S5).

[0081] In this step, the optical path length of the second beam is adjusted based on the height difference Δh detected in step S1 so that the second overlay mark OM2 is in focus. Since the second overlay mark OM2 is formed in the lower layer, the optical path length of the second beam must be increased.

[0082] Next, the second beam that has passed through the telecentric lens is imaged onto a second detector (S6).

[0083] In this step, a second beam of a wavelength band adapted for acquiring an image of the second overlay mark OM2 is imaged onto a second detector 50.

[0084] Next, a first overlay mark image I1 is generated from the first detector, and a second overlay mark image I2 is generated from the second detector (S7).

[0085] In this step, a first overlay mark image I1 is generated from the first detector, in which the first overlay mark OM1 is clearly displayed.

[0086] Because there is a large height difference between the first overlay mark OM1 and the second overlay mark OM2, when the first overlay mark OM1 is in focus, the second overlay mark OM2 is not in focus, so the second overlay mark OM2 appears blurry in the first overlay mark image I1.

[0087] Also, a second overlay mark image I2 is generated from the second detector, in which the second overlay mark OM2 is clearly displayed, while the first overlay mark OM1 is blurred in the second overlay mark image I2.

[0088] Because the second beam passes through the telecentric lens, the magnification of the second overlay mark image I2 does not change even if the optical path of the second beam changes. If the telecentric lens is not used, the magnification of the second overlay mark image I2 changes due to the change in the optical path length, so it is difficult to obtain an overlay mark image by combining the first overlay mark image I1 and the second overlay mark image I2.

[0089] In this case, in some embodiments, the first detector 40 and the second detector 50 can be synchronized such that the first overlay mark image I1 and the second overlay mark image I2 are generated simultaneously in order to minimize errors that may occur due to vibrations during the overlay measurement process.

[0090] Then, the first overlay mark image I1 and the second overlay mark image I2 are used to measure the overlay error.

[0091] The above-described embodiments are merely preferred embodiments of the present invention, and the scope of the present invention is not limited to the described embodiments. Various changes, modifications, or substitutions are possible 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 such embodiments belong to the scope of the present invention. [Explanation of symbols]

[0092] 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 Second Detector 60 Imaging Optical System 70 Telecentric imaging optical system

Claims

1. 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: a height difference detection optical system configured to detect a height difference (Δh) between the first overlay mark and the second overlay mark; an illumination optical system 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; imaging optics configured to image the first beam onto the first detector; an optical path adjusting unit that adjusts an optical path length of the second beam based on the height difference; and a telecentric imaging optical system that is disposed between the main beam splitter and the second detector and includes a telecentric lens that images the second beam onto the second detector.

2. The optical path adjusting unit is at least one mirror disposed between the main beam splitter and the second detector to reflect the second beam toward the second detector; a mirror stage configured to linearly move at least one of the mirrors to adjust the optical path length of the second beam; The overlay measurement apparatus of claim 1 , further comprising: a controller configured to control the mirror stage based on the height difference.

3. 3. The overlay measurement apparatus of claim 2, 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.

4. the imaging optical system further comprises a first optical filter disposed in front of the first detector and configured to adjust a central wavelength and a bandwidth of the first beam for acquiring the first overlay mark image; 2. The overlay measurement apparatus of claim 1, wherein the telecentric imaging optical system further comprises a second optical filter disposed in front of the second detector and adjusting a central wavelength and a bandwidth of the second beam for acquiring the second overlay mark image.

5. 5. The overlay measurement apparatus of claim 4, wherein the first optical filter and the second optical filter are linear or rotary variable filters.

6. 2. The overlay measurement apparatus of claim 1, wherein said first detector and said second detector are synchronized such that said first overlay mark image and said second overlay mark image are generated simultaneously.

7. 1. An overlay measurement method for measuring an inter-layer overlay error of a sample having an overlay mark, the inter-layer overlay error including a first overlay mark and a second overlay mark formed on different layers, the first overlay mark and the second overlay mark being formed on different layers, the method comprising: detecting a height difference (Δh) between the first overlay mark and the second overlay mark; shining illumination onto an overlay mark on the sample; splitting reflected light from the overlay mark into a first beam and a second beam; imaging the first beam onto a first detector; adjusting an optical path length of the second beam based on the height difference (Δh) so as to focus on the second overlay mark; imaging the second beam through a telecentric lens and the adjusted length of the optical path onto a second detector; generating a first overlay mark image with the first detector focused on the first overlay mark, and generating a second overlay mark image with the second detector focused on the second overlay mark.

8. 8. The overlay measurement method of claim 7, wherein 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 optical path length of the second beam is adjusted such that the optical path of the extended second beam is longer than the optical path of the first beam.

9. adjusting a central wavelength and a bandwidth of the first beam for acquiring the first overlay mark image; 8. The method of claim 7, further comprising the step of: adjusting a central wavelength and a bandwidth of the second beam for acquiring the second overlay mark image.

10. 10. The overlay measurement method of claim 9, wherein the central wavelength of the first beam and the central wavelength of the second beam are different from each other.

11. 8. The method of overlay measurement of claim 7, wherein the first detector and the second detector are synchronized such that the first overlay mark image and the second overlay mark image are generated simultaneously.

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