Overlay measurement device, focus control method of overlay measurement device for tool-induced shift measurement, and focus control program of overlay measurement device for tool-induced shift measurement

Abstract

The present invention provides a focus control method of an overlay measurement device for tool-induced shift measurement, the method comprising the steps of: acquiring a first signal, which is a signal from an automatic focusing device when a corresponding site is focused for each site of a reference field of a reference wafer in a non-rotated state; acquiring a second signal, which is a signal from the automatic focusing device when a corresponding site is focused for each site of the reference field after the reference wafer is rotated 180 degrees; matching the first signal and the second signal to a corresponding site and storing same; positioning, within the field of view of the overlay measurement device, a site to be measured of a wafer to be measured; and, if the wafer to be measured is in a non-rotated state, focusing on the basis of the first signal matched to the site to be measured, and, if the wafer to be measured is in a 180 degree-rotated state, focusing on the basis of the second signal matched to the site to be measured.

Description

Overlay measuring device, focus control method of overlay measuring device for tool-induced shift measurement and focus control program of overlay measuring device for tool-induced shift measurement

[0001] The present invention relates to an overlay measuring device, a focus control method of the overlay measuring device for tool-induced shift measurement, and a focus control program of the overlay measuring device for tool-induced shift measurement.

[0002] Multiple pattern layers are sequentially formed on a semiconductor substrate. Furthermore, through processes such as double patterning, a single layer of circuitry can be divided into two patterns. These pattern layers, or multiple patterns within a single layer, must be precisely formed at predetermined locations to manufacture the desired semiconductor device.

[0003] Therefore, to ensure that the pattern layers are aligned accurately, overlay marks that are formed simultaneously with the pattern layers are used.

[0004] The method for measuring overlay using an overlay mark is as follows. First, a structure that is part of the overlay mark is formed simultaneously with the pattern layer formed in a previous process, such as an etching process. Then, in a subsequent process, such as a photolithography process, the remaining structure of the overlay mark is formed in photoresist.

[0005] And, through the overlay measurement device, an image of the overlay structure of the pattern layer formed in the previous process (an image is obtained by penetrating the photoresist layer) and the overlay structure of the photoresist layer are obtained, and an offset value between the centers of these images is measured to measure the overlay error value.

[0006] More specifically, Japanese Patent Application Laid-Open No. 2020-112807 discloses a method for capturing an image of an overlay mark formed on a substrate, selecting a plurality of working zones from the captured image, forming a signal having information about each of the selected working zones, and comparing them to determine relative misalignment between different layers or different patterns.

[0007] Fig. 1 is a plan view of an example of an overlay mark. The overlay mark (1) illustrated in Fig. 1 has four working zone sets (4, 5, 6, 7). Each working zone set (4, 5, 6, 7) has two working zones that are arranged diagonally from each other. Each working zone set (4, 5, 6, 7) is used to measure an overlay error in the X-axis or Y-axis direction of a pattern layer formed together with the corresponding working zone set. In order to prevent interference from occurring, structures (2) formed together with the first pattern layer and structures (3) formed together with the second pattern layer are arranged so as not to overlap each other.

[0008] Each working zone includes bars arranged at regular intervals from the center of the overlay mark (1) to the periphery of the overlay mark (1). Therefore, using an overlay measuring device, periodic signals, as illustrated in Fig. 2, can be obtained from two working zones belonging to a set of working zones (4, 5, 6, 7). The graph of Fig. 2 can be obtained, for example, from a selected portion (8) of Fig. 1.

[0009] In the graph of Fig. 2, peaks appear in areas where bars are arranged. Since the conventional overlay mark (1) has bars arranged periodically, the acquired signal also has periodicity. Furthermore, the overlay error is measured through correlation analysis of two periodic signals acquired from two selected regions (8, 8').

[0010] Measuring these overlay errors requires high-quality overlay measurement devices to meet the demands of advanced lithography processes. During overlay error measurement, defects (e.g., aberrations) in the optical components of the overlay measurement device can cause tool-induced shift (TIS). These optical defects in the overlay measurement device can cause a shift between the actual overlay error and the measured overlay error.

[0011] Tool-induced shift measurement requires repeated overlay error measurements in the non-rotated and 180-degree rotated wafer states. The tool-induced shift can be calculated by dividing the sum of the overlay error values ​​in the non-rotated and 180-degree rotated wafer states by 2. Ideally, the overlay error values ​​in the non-rotated and 180-degree rotated states are equal in magnitude and opposite in sign, so the tool-induced shift is zero.

[0012]

[0013] *Overlay error measurements for tool-induced shift measurements are made at multiple sites (overlay marks) within the reference field.

[0014] Fig. 3 is a drawing showing an example of a wafer. As illustrated in Fig. 3, the semiconductor wafer includes a plurality of fields (F). In one field (F), there are a plurality of sites (S1, S2, S3, S4) (four in Fig. 3). An overlay mark is positioned on each site (S1, S2, S3, S4). The reference field is usually positioned at the center of the wafer. Sites having the same location within each field (F) are assigned the same site index. That is, when the fields (F) are overlapped, the overlapping sites have the same site index. The measurement sites (S1, S2, S3, S4) of the semiconductor wafer illustrated in Fig. 3 may have site indices ranging from 1 to 4.

[0015] In order to measure the overlay error for tool-induced shift measurement, an image of the overlay mark must be acquired. To acquire an image of the overlay mark, the 'measurement focus' of the site must be found. The 'measurement focus' is the focus for acquiring the optimal overlay mark image and may differ from the 'standard focus' found using an autofocus device. Finding the 'measurement focus' takes a relatively long time. Therefore, a method is used in which the 'reference signal value', which is the signal value from the autofocus device in the 'standard focus' state, is acquired in advance, and then the position of the objective lens is adjusted so that the signal value from the autofocus device matches the 'reference signal value' before acquiring an image of the overlay mark.

[0016] Previously, the "reference signal value" of a specific site found in the non-rotated state of the wafer was used as is for measuring the overlay error in the 180-degree rotation state. However, as semiconductor devices become smaller and more integrated, the overlay mark becomes smaller, which raises the problem that the area illuminated by the light used in the autofocus device may become larger than the size of the overlay mark. If it illuminates other surrounding overlay marks or the boundary of the scribe line beyond the overlay mark, the signal from the autofocus device is likely to be distorted. In addition, because the surrounding environments in the non-rotated state and the 180-degree rotation state are different, the tool-induced shift value measured by the conventional method may also be distorted. Therefore, if the tool-induced shift value measured by the conventional method is applied to correct the measured overlay error value, an inaccurate overlay error value may be obtained.

[0017] Fig. 4 is a diagram showing an overlay mark and its surroundings in a non-rotated state and a 180-degree rotated state. Fig. 4 (a) shows the non-rotated state, and (b) shows the state where the wafer is rotated 180 degrees. As shown in Fig. 4, the lines (L) located above the overlay mark (OM) in the non-rotated state are located below the overlay mark (OM) in the 180-degree rotated state. In addition, the laser beam (LB), which is the illumination of the autofocus device, illuminates the surrounding lines (L) beyond the overlay mark (OM). Therefore, the reflected light from the surrounding lines (L) is also transmitted to the autofocus device.

[0018] Fig. 5 is a graph showing the distribution of differences between the overlay error values ​​for each site of the same wafer measured by two different overlay measurement devices using a conventional method. Fig. 5 is illustrated based on a wafer in which each field has 25 sites. In the graph of Fig. 5, the X-axis is the site index. The Y-axis is the difference value between the overlay error values ​​obtained by each of the two devices. The distribution of the Y values ​​is the distribution between sites located in different fields having the same site index. The overlay error value used to illustrate Fig. 5 is not a general overlay error value, but rather a value obtained by subtracting the overlay error value in a 180-degree rotated state from the overlay error value in a non-rotated state and dividing it by 2.

[0019] In Fig. 5, the sites within the box (sites 2, 3, 7, 8, and 9) are sites with significant differences in their surrounding environments between the non-rotated and 180-degree rotated states. As can be seen in Fig. 5, when using the conventional method, the difference values ​​of the overlay error values ​​of these sites show a different distribution from other sites. The closer the average of the difference values ​​of sites with the same site index is to 0, the smaller the dispersion of the difference values ​​of sites with the same site index, and the more similar the distribution of sites with different site indices are to each other, the more accurate the overlay error measurement is.

[0020] [Prior Art Literature]

[0021] (Patent Document 1) Japanese Patent Publication No. 2020-112807

[0022] (Patent Document 2) Korean Patent Publication No. 10-2001-0092740

[0023] (Patent Document 3) Korean Patent No. 10-2236184

[0024] (Patent Document 4) Korean Patent No. 10-2524462

[0025] (Patent Document 5) Korean Patent No. 10-1869573

[0026] The present invention is intended to improve the above-described problems, and an object of the present invention is to provide an overlay measuring device capable of improving distortion of tool-induced shift caused by an area illuminated by a light used in an autofocus device becoming larger than the size of an overlay mark.

[0027] In addition, another purpose is to provide a focus control method of an overlay measuring device for tool-induced shift measurement and a focus control program of an overlay measuring device for tool-induced shift measurement.

[0028] In order to achieve the above-described object, the present invention provides a focus control method of an overlay measurement device for tool-induced shift measurement, comprising the steps of: obtaining a first signal, which is a signal from an auto-focus device when a corresponding site is in focus, for each site of a reference field of a reference wafer in an unrotated state; obtaining a second signal, which is a signal from the auto-focus device when a corresponding site is in focus, for each site of the reference field after rotating the reference wafer by 180 degrees; matching the first signal and the second signal with the corresponding site and storing them; positioning a measurement target site of a measurement target wafer within a field of view of the overlay measurement device; and focusing based on the first signal matched with the measurement target site when the measurement target wafer is in an unrotated state, and focusing based on the second signal matched with the measurement target site when the measurement target wafer is in a 180-degree rotated state.

[0029] In addition, the autofocus device is a phase difference detection autofocus system, and the first signal and the second signal are signals based on phase difference, and a focus control method of an overlay measuring device is provided.

[0030] In addition, the above measurement target site provides a focus control method of an overlay measurement device that is a site in the reference field of the reference wafer or a field different from the reference field.

[0031] In addition, the present invention provides a focus control method of an overlay measurement device in which the measurement target wafer is the reference wafer or another wafer belonging to the same lot as the reference wafer.

[0032] In addition, a focus control method of an overlay measurement device is provided to confirm whether the wafer to be measured is rotated through the position of a flat zone or notch of the wafer.

[0033] In addition, the first signal matched with the measurement target site provides a focus control method of an overlay measurement device, wherein the first signal is acquired from a site within the reference field having the same location within the field as the measurement target site.

[0034] In addition, the present invention provides an overlay measuring device comprising: an objective lens; a lens focus actuator configured to move the objective lens to adjust a distance between a wafer and the objective lens; an auto-focus device that outputs a signal according to the distance between the objective lens and the wafer; and a controller communicatively coupled to the lens focus actuator and the auto-focus device.

[0035] Here, the controller includes a memory having instructions stored therein, and a processor configured to execute the instructions, wherein the instructions cause the processor to perform the following steps: obtaining a first signal, which is a signal from the auto-focus device when each site of a reference field of a reference wafer in an unrotated state is in focus; obtaining a second signal, which is a signal from the auto-focus device when each site of the reference field is in focus after rotating the reference wafer by 180 degrees; matching the first signal and the second signal with the corresponding site and storing them; positioning a measurement target site of a measurement target wafer within a field of view of the overlay measurement device; and, when the measurement target wafer is in an unrotated state, moving the objective lens to focus based on the first signal matched with the measurement target site, and when the measurement target wafer is in a 180 degree rotated state, moving the objective lens to focus based on the second signal matched with the measurement target site.

[0036] In addition, the present invention provides a program stored in a storage medium for executing a method for controlling the focus of an overlay measurement device using a computing device, the program comprising: a step of obtaining a first signal, which is a signal from an auto-focus device, when a site in a reference field of a non-rotated reference wafer is in focus; a step of obtaining a second signal, which is a signal from the auto-focus device, when a site in the reference field is in focus after rotating the reference wafer by 180 degrees; a step of matching the first signal and the second signal with the corresponding site and storing them; a step of positioning a measurement target site of a measurement target wafer within a field of view of the overlay measurement device; and a step of focusing based on the first signal matched with the measurement target site when the measurement target wafer is in an non-rotated state, and focusing based on the second signal matched with the measurement target site when the measurement target wafer is in a 180 degree rotated state.

[0037] According to the present invention, the distortion of tool-induced shift caused by the area illuminated by the light used in the autofocus device becoming larger than the size of the overlay mark is improved, thereby obtaining a more accurate tool-induced shift value.

[0038] Using these tool-induced shift values ​​to compensate for the overlay error allows for more accurate overlay error measurements even on wafers with small overlay marks.

[0039] Figure 1 is a plan view of an example of an overlay mark.

[0040] Figure 2 shows a signal obtained from one working zone of the overlay mark illustrated in Figure 1.

[0041] Figure 3 is a drawing showing an example of a wafer.

[0042] Figure 4 is a drawing showing the overlay mark and the surrounding environment in a non-rotated state and a 180-degree rotated state.

[0043] Figure 5 is a graph showing the distribution of difference values ​​between site-by-site overlay error values ​​of the same wafer measured by two different overlay measurement devices using a conventional method.

[0044] Figure 6 is a schematic diagram of an overlay measuring device according to one embodiment of the present invention.

[0045] FIG. 7 is a flowchart of a focus control method of an overlay measurement device for tool-induced shift measurement according to one embodiment of the present invention.

[0046] Figure 8 shows an example of a table in which the first signal and the second signal are stored.

[0047] FIG. 9 is a graph showing the distribution of difference values ​​between site-by-site overlay error values ​​of the same wafer measured by two different overlay measurement devices using the focus control method of the present invention.

[0048] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art. Therefore, the shapes of elements in the drawings are exaggerated to emphasize a clearer description, and elements indicated by the same reference numerals in the drawings represent the same elements.

[0049] FIG. 6 is a schematic diagram of an overlay measurement device according to an embodiment of the present invention. As illustrated in FIG. 6, the overlay measurement device (100) includes an illumination optical system (20) for illuminating an overlay mark on a semiconductor wafer (W) on a stage (10) that supports a semiconductor wafer, an imaging optical system (30) for focusing reflected light from the overlay mark to form an overlay mark image, an image detector (40) for obtaining an overlay mark image formed by the imaging optical system (30), an autofocus device (50), and a controller (60).

[0050] The overlay measurement device (100) is used to measure the overlay error between multiple consecutive pattern layers.

[0051] The stage (10) can move in the X and Y directions, which are orthogonal to each other, by a horizontal driving unit. The stage (10) serves to support and horizontally move a semiconductor wafer (W). The stage (10) may be equipped with a vacuum chuck for fixing the semiconductor wafer (W).

[0052] The illumination optical system (20) can be configured using various optical elements. For example, the illumination optical system (20) can include an illumination source (21), a beam splitter (23), and an objective lens (25). In addition, it can further include other optical elements such as other lenses or apertures.

[0053] The illumination source (21) serves to generate illumination that illuminates the overlay mark. The illumination source (21) may include a light source capable of generating light with a wide wavelength band and variable optical filters capable of adjusting the wavelength band of the transmitted light. A laser diode or a light-emitting diode may be used as the light source. The illumination source (21) can generate illumination with various wavelength bands by adjusting the wavelength band of light from the light source by combining optical filters.

[0054] A beam splitter (23) is placed between the illumination source (21) and the objective lens (25), and serves to transmit illumination from the illumination source (21) to the objective lens (25).

[0055] The objective lens (25) focuses light onto a measurement position on the surface of a semiconductor wafer (W) and collects reflected light reflected at the measurement position. The objective lens (25) is installed on a lens focus actuator (27). The lens focus actuator (27) is used to adjust the distance between the objective lens (25) and the semiconductor wafer (W). Focus control is achieved by movement of the objective lens (25) in the Z direction.

[0056] The imaging optical system (30) can be configured using various optical elements. For example, the imaging optical system (30) can include a hot or cold mirror (31) and a tube lens (33). In addition, the imaging optical system (30) can use the objective lens (25) and beam splitter (23) of the illumination optical system (20). In addition, other optical elements such as other lenses or apertures can be further included.

[0057] A hot or cold mirror (31) serves to prevent the light used in the autofocus device (50) from being directed to the image detector (40). A hot mirror has high transmittance for short-wavelength light and reflects long-wavelength light. Conversely, a cold mirror has high transmittance for long-wavelength light and reflects short-wavelength light. When the light used in the autofocus device (50) has a shorter wavelength than the light for image acquisition, a cold mirror is used to reflect the light reflected by the light used in the autofocus optical system (50) toward the autofocus device (50). Conversely, when the light used in the autofocus device (50) has a longer wavelength than the light for image acquisition, a hot mirror is used to reflect the light reflected by the light used in the autofocus device (50) toward the autofocus device (50).

[0058] The reflected light collected from the objective lens (25) passes through the beam splitter (23) and is then focused onto the image detector (40) by the tube lens (33).

[0059] The image detector (40) receives reflected light from the overlay mark by illumination and generates an overlay mark image. The image detector (40) may be a CCD (Charge-Coupled Device) camera or a CMOS (Complementary Metal-Oxide Semiconductor) camera. The image detector (40) may use an image pickup device equipped with an RGB (Red Green Blue) color filter, or may use a monochrome image pickup device.

[0060] The autofocus device (50) serves to provide information regarding the Z-direction position of the wafer (w) surface required to focus on the measurement target. The autofocus device (50) provides, for example, a signal according to the distance between the objective lens (25) and the wafer (w) surface. Various types of autofocus systems can be used as the autofocus device (50). For example, a phase detection autofocus system, a contrast detection autofocus system, a hybrid autofocus system, etc. can be used.

[0061] The phase detection autofocus system uses two or more sensors to detect the phase difference between light rays entering the overlay measurement device (100) from the wafer (w), which is the subject of the photograph, and can determine the direction and distance that the objective lens (25) should move.

[0062] Contrast-detection autofocus systems analyze the contrast between bright and dark areas of an image to determine focus. The system determines when the image is in focus when contrast is maximized.

[0063] The hybrid autofocus system uses phase detection to fine-tune the focus position after obtaining the approximate focus distance using contrast detection.

[0064] The controller (60) is installed to be able to communicate with the lens focus actuator (27), the image detector (40), and the autofocus device (50) via wired or wireless means. The controller (60) may include hardware such as a processor, memory, a fixed storage device (ROM), a storage device such as a hard disk or SSD, and a wired or wireless communication device. In addition, the controller includes a program such as firmware or software installed in a storage medium such as a memory, a fixed storage device, or a storage device.

[0065] A computing device such as an MCU (Micro controller unit), desktop computer, laptop computer, smartphone, or smart pad can be used as the controller (60).

[0066] The controller (60) can cause the processor to perform the steps of FIG. 7 below through the program's commands.

[0067] FIG. 7 is a flowchart of a focus control method of an overlay measurement device for tool-induced shift measurement according to one embodiment of the present invention.

[0068] As illustrated in FIG. 7, the controller (60) performs a step (S1) of acquiring a first signal, which is a signal from an auto-focus device when the focus is on each site of the reference field of the non-rotated reference wafer.

[0069] A reference wafer is one of multiple wafers belonging to the same lot. The reference wafer contains multiple fields. Each field contains multiple sites (e.g., 25 sites). Overlay marks are located on the sites. The reference field is usually located at the center of the wafer.

[0070] In this step, a first signal, which is a signal of an autofocus device (50) when the overlay mark of each site within the reference field is focused, is acquired. If a phase detection autofocus system is used as the autofocus device (50), the phase value output from the phase detection autofocus system when aligned with the 'measurement focus', which is the focus applied when acquiring an overlay mark image for actual overlay error measurement, can become the first signal.

[0071] In a typical imaging system, the focus found through an auto-focus device (50) becomes the 'measurement focus', but since the overlay mark includes overlay structures formed with different pattern layers, the 'measurement focus' may be located between the overlay structure formed on the previous pattern layer and the overlay structure formed on the current pattern layer. In particular, when the height difference between the overlay structures is large, the difference between the focus found through the auto-focus device (50) and the 'measurement focus' may be large. The 'measurement focus' can be found by evaluating the quality of the acquired overlay mark image using various quality metrics.

[0072] When using a phase detection autofocus system with an autofocus device (50), in a normal imaging system, focus can be considered to be achieved when the phase difference becomes 0, but in the case of an overlay mark, focus ('measured focus') can be achieved when the phase difference is not 0.

[0073] After acquiring the first signal from one site, the next site is positioned at the center of the field of view of the overlay measurement device (100) using a pattern recognition unit (PRU). Then, the first signal from that site is acquired in the same manner.

[0074] This process is repeated until first signals are acquired at all measurement target sites within the reference field. The first signals may vary from site to site depending on the type of pattern layers on which the overlay marks are formed, height differences, etc.

[0075] Next, the controller (60) rotates the reference wafer by 180 degrees and then performs a step (S2) of acquiring a second signal from the auto focus device (50) when the focus is on each site of the reference field.

[0076] In this step, first, the stage on which the reference wafer is mounted is rotated 180 degrees.

[0077] And, a second signal, which is a signal of an auto focus device (50) when the overlay mark of each site within the reference field used in step S1 is focused, is acquired.

[0078] Ideally, the second signal for the overlay mark on the same site would match the first signal. However, in practice, the second signal and the first signal may differ. For example, if the size of the laser line used as the illumination in the autofocus device (50) is larger than the size of the overlay mark, the laser may be irradiated beyond the overlay mark on the target site to other surrounding overlay marks, patterns, etc. The reflected light from these surrounding marks or patterns may affect the signal of the autofocus device (50). The degree of this effect may vary depending on the rotation angle of the wafer.

[0079] Sites located in the center of the reference field may have similar first and second signals, but sites located above or below the reference field, where the environment around the overlay mark changes significantly depending on the rotation angle, may have a very large difference between the second and first signals.

[0080] This step is performed in the same way as step S1.

[0081] Next, the controller (60) performs a step (S3) of matching the first signal and the second signal with the corresponding site and storing them.

[0082] For example, as illustrated in FIG. 8, it may be stored in the memory of the controller (60) or another storage device in the form of a table including a recipe ID, an overlay mark ID, a site index, a first signal, a second signal, etc. The table stores the first signals and second signals of all sites within the reference field.

[0083] Next, the controller (60) performs a step (S4) of positioning the measurement target site of the measurement target wafer within the field of view of the overlay measurement device (100).

[0084] In this step, the controller (60) can move the wafer by moving the stage (10) that supports the wafer to be measured in a plane. The wafer to be measured may be a reference wafer or another wafer belonging to the same lot as the reference wafer.

[0085] This step may include a global alignment step and a site alignment step. The controller (60) uses a pattern recognition unit to position the overlay mark of the measurement target site within the field of view of the overlay measurement device (100).

[0086] The measurement target sites may be sites of the reference field of the reference wafer used to acquire the first and second signals or other fields. They may also be sites of fields of other wafers belonging to the same lot manufactured using the same process.

[0087] If the site index is the same, the first and second signals are almost identical even if the site belongs to a different field of the same wafer or a field of a different wafer of the same lot. Therefore, the first and second signal information acquired in the reference field can be applied to the site of a different field of the same wafer or a field of a different wafer of the same lot.

[0088] Next, the controller (60) performs a step (S5) of moving the objective lens (25) to focus based on a first signal matched with the measurement target site if the measurement target wafer is not rotated, and moving the objective lens to focus based on a second signal matched with the measurement target site if the measurement target wafer is rotated 180 degrees.

[0089] The controller (60) determines whether the wafer to be measured, for which tool-induced shift measurement is required, is in a non-rotated state or a 180-degree rotated state. The controller (60) can determine the rotational state of the wafer to be measured by, for example, using a proximity sensor or the like to determine the position of the flat zone or notch of the wafer to be measured.

[0090] If the wafer to be measured is not rotated, the controller (60) moves the objective lens (25) to focus using the first signal that matches the site with the same site index as the corresponding measurement target site stored in the table. If the wafer to be measured is rotated 180 degrees, the controller moves the objective lens (25) to focus using the second signal stored in the table.

[0091] The controller (60) can move the objective lens (25) to focus until the signal output from the autofocus device (50) matches the first signal (the second signal if rotated by 180 degrees). The controller (60) can adjust the Z-axis position of the objective lens (25) by controlling the lens focus actuator (27).

[0092] When the movement of the objective lens (25) is completed, the illumination optical system (20) is used to illuminate the measurement target site, and the reflected light from the overlay mark is collected by the imaging optical system (30) to image the overlay mark image onto the image detector (40), thereby obtaining the overlay mark image.

[0093] Using the overlay mark image acquired in the non-rotated state, the X-direction overlay error and the Y-direction overlay error are measured, respectively. Then, using the overlay mark image acquired in the same way at the same site in the 180-degree rotated state, the X-direction overlay error and the Y-direction overlay error are measured again, respectively.

[0094] The X-direction tool-induced shift of the overlay mark (site) in question can be, for example, the average of the sum of the X-direction overlay error in the non-rotated state and the X-direction overlay error in the 180-degree rotated state. Also, the Y-direction tool-induced shift can be the average of the sum of the Y-direction overlay error in the non-rotated state and the Y-direction overlay error in the 180-degree rotated state. Ideally, the X-direction tool-induced shift and the Y-direction tool-induced shift are zero.

[0095] The X-direction tool-induced shift and the Y-direction tool-induced shift can be used to compensate for the overlay error values ​​measured at the site.

[0096] Fig. 9 is a graph showing the distribution of differences between overlay error values ​​for each site of the same wafer measured by two different overlay measurement devices using the focus control method of the present invention. In the graph of Fig. 9, the X-axis represents the site index, and the Y-axis represents the difference value of the overlay error values ​​between the overlay measurement devices. Similar to Fig. 5, the graph shows the distribution of overlay error values ​​measured at sites having the same site index of multiple fields of one wafer.

[0097] As illustrated in Fig. 9, when the focus control method of the present invention is applied, the difference values ​​of the overlay error values ​​between sites with different site indices of the devices exhibit a similar distribution. In other words, the site-specific deviation caused by distortion due to the illumination of the autofocus device is reduced.

[0098] The embodiments described above merely describe preferred embodiments of the present invention, and the scope of the present invention is not limited to the described embodiments, and various changes, modifications, 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 such embodiments fall within the scope of the present invention.

[0099] [Explanation of symbols]

[0100] w: wafer

[0101] 10: Stage

[0102] 20: Illumination optics

[0103] 30: Focusing optical system

[0104] 40: Image detector

[0105] 50: Autofocus device

[0106] 60: Controller

Claims

1. A focus control method of an overlay measuring device for tool-induced shift measurement, A step of obtaining a first signal, which is a signal from an auto-focus device when the site is focused on each site of the reference field of the non-rotated reference wafer, wherein the illumination of the auto-focus device is a long illumination that extends beyond the overlay mark formed at the site; A step of obtaining a second signal from the auto-focus device when each site of the reference field is focused after rotating the reference wafer by 180 degrees, wherein the illumination of the auto-focus device is illumination with a length that exceeds the overlay mark formed at the site; A step of matching the first signal and the second signal with the corresponding site and storing them, A step of positioning a measurement target site of a measurement target wafer within the field of view of the above overlay measurement device, A focus control method of an overlay measurement device, comprising the step of focusing based on the first signal matched with the measurement target site when the measurement target wafer is not rotated, and focusing based on the second signal matched with the measurement target site when the measurement target wafer is rotated by 180 degrees.

2. In paragraph 1, A focus control method of an overlay measuring device, wherein the autofocus device is a phase difference detection autofocus system, and the first signal and the second signal are signals based on phase difference.

3. In paragraph 1, A focus control method of an overlay measurement device, wherein the measurement target site is a site in the reference field of the reference wafer or a field different from the reference field.

4. In paragraph 1, A focus control method of an overlay measurement device in which the above measurement target wafer is the reference wafer or another wafer belonging to the same lot as the reference wafer.

5. In paragraph 1, A focus control method of an overlay measurement device that checks whether the above measurement target wafer is rotated through the position of a flat zone or notch of the wafer.

6. In paragraph 1, A focus control method of an overlay measurement device, wherein the first signal matched with the measurement target site is a first signal obtained from a site within the reference field that has the same location within the field as the measurement target site.

7. As an overlay measuring device, With an objective lens, A lens focus actuator configured to move the objective lens and adjust the distance between the wafer and the objective lens, An auto-focus device that outputs a signal according to the distance between the objective lens and the wafer, A controller communicatively coupled to the lens focus actuator and the autofocus device, The controller includes a memory having instructions stored therein and a processor configured to execute the instructions, wherein the instructions cause the processor to: A step of obtaining a first signal from the auto-focus device when the focus is on each site of the reference field of the non-rotated reference wafer, wherein the illumination of the auto-focus device is a long illumination that extends beyond the overlay mark formed at the site; A step of obtaining a second signal from the auto-focus device when each site of the reference field is focused after rotating the reference wafer by 180 degrees, wherein the illumination of the auto-focus device is illumination with a length that exceeds the overlay mark formed at the site; A step of matching the first signal and the second signal with the corresponding site and storing them, A step of positioning a measurement target site of a measurement target wafer within the field of view of the above overlay measurement device, An overlay measurement device that performs a step of moving the objective lens to focus based on the first signal matched with the measurement target site when the measurement target wafer is in a non-rotated state, and moving the objective lens to focus based on the second signal matched with the measurement target site when the measurement target wafer is in a 180-degree rotated state.

8. A program stored in a storage medium for executing a method of controlling the focus of an overlay measuring device using a computing device, A step of obtaining a first signal, which is a signal from an auto-focus device when the site is focused on each site of the reference field of the non-rotated reference wafer, wherein the illumination of the auto-focus device is a long illumination that extends beyond the overlay mark formed at the site; A step of obtaining a second signal from the auto-focus device when each site of the reference field is focused after rotating the reference wafer by 180 degrees, wherein the illumination of the auto-focus device is illumination with a length that exceeds the overlay mark formed at the site; A step of matching the first signal and the second signal with the corresponding site and storing them, A step of positioning a measurement target site of a measurement target wafer within the field of view of the above overlay measurement device, A program for controlling the focus of an overlay measurement device that performs a step of focusing based on the first signal matched with the measurement target site when the measurement target wafer is not rotated, and focusing based on the second signal matched with the measurement target site when the measurement target wafer is rotated by 180 degrees.

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