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

Abstract

The invention provides a focus control method of an overlay measurement device, and the overlay measurement device is used for tool induced displacement measurement. The focus control method of the overlay measurement apparatus includes: a step of acquiring, for each point of a reference field of a reference wafer in an unrotated state, a first signal as a signal from an automatic focusing device when focused at the corresponding point; after rotating the reference wafer by 180 degrees, acquiring a second signal, which is a signal from the automatic focusing device at the time of focusing at the corresponding point, for each of the points of the reference field; matching and storing the first signal and the second signal with corresponding point locations; a step in which a measurement target point of a measurement target wafer is positioned within the field of view of the overlay measurement device; and when the wafer to be measured is in a non-rotating state, focusing according to the first signal matched with the point location of the wafer to be measured, and when the wafer to be measured is in a 180-degree rotating state, focusing according to the second signal matched with the point location of the wafer to be measured.

Description

Technical Field

[0001] This invention relates to a calendering measuring device, a focus control method for a calendering measuring device for tool-induced displacement measurement, and a focus control program for a calendering measuring device for tool-induced displacement measurement. Background Technology

[0002] Multiple patterned layers are sequentially formed on a semiconductor substrate. Furthermore, through methods such as double patterning, the circuitry of a single layer can be formed as two separate patterns. The desired semiconductor device can only be manufactured when these patterned layers, or multiple patterns within a single layer, are precisely formed at predetermined locations.

[0003] Therefore, in order to confirm whether the pattern layer is accurately aligned, overlay marks formed simultaneously with the pattern layer are used.

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

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

[0006] More specifically, Japanese Patent Publication 2020-112807 discloses a method that captures an image of overlay marks formed on a substrate, selects multiple working areas in the captured image, forms an information signal for each selected working area, and compares these signals to determine the relative misalignment between different layers or different patterns.

[0007] Figure 1 This is a plan view of an example of an engraved mark. Figure 1 The overlay mark 1 shown includes four working zone groups 4, 5, 6, and 7. Furthermore, each working zone group 4, 5, 6, and 7 includes two working zones arranged diagonally opposite each other. Each working zone group 4, 5, 6, and 7 is used to measure the overlay error of the patterned layer formed together with the corresponding working zone group in the X-axis or Y-axis direction. To prevent interference, the structure 2 formed with the first patterned layer and the structure 3 formed with the second patterned layer are configured not to overlap.

[0008] Each working area includes strips arranged at constant intervals from the center of overlay mark 1 to the outer contour of overlay mark 1. Therefore, using the overlay measuring device, samples can be obtained from the two working areas belonging to working area groups 4, 5, 6, and 7, respectively. Figure 2 The periodic signal shown. Figure 2 For example, a chart can be obtained from Figure 1 The selected area 8 is obtained.

[0009] exist Figure 2 In the chart, the peak appears in the section with the arranged bars. Previously, due to the periodic arrangement of the bars, the acquired signal also exhibited periodicity. Furthermore, the overlay error was measured by performing correlation analysis on two periodic signals acquired from two selected regions 8 and 8'.

[0010] To meet the requirements of advanced photolithography processes, such overlay error measurement necessitates a high-quality overlay measurement device. When measuring overlay error, defects (e.g., aberrations) in the optical elements constituting the overlay measurement device can cause tool-induced shift (TIS). Such optical defects in the overlay measurement device can lead to a displacement between the actual overlay error and the measured overlay error.

[0011] Tool-induced displacement measurement requires repeated overlay error measurements in both the unrotated and 180-degree rotated states of the wafer. The tool-induced displacement can be the sum of the overlay error values ​​in the unrotated and 180-degree rotated states, divided by 2. Ideally, since the overlay error values ​​in the unrotated and 180-degree rotated states are equal in magnitude but opposite in sign, the tool-induced displacement is zero.

[0012] Overlay error measurements for tool-induced displacement measurements are performed at multiple points (overlay marks) located within the reference field.

[0013] Figure 3 This is a diagram showing an example of a wafer. (For example...) Figure 3 As shown, a semiconductor wafer includes multiple fields F. Multiple ( ) exist within a single field F. Figure 3 There are four reference fields (S1, S2, S3, and S4). Each reference field has an overlay mark. The reference field is typically located at the center of the wafer. Reference fields in the same position within each field F are assigned the same reference index. That is, when fields F are stacked, overlapping reference fields have the same reference index. Figure 3 The measurement points S1, S2, S3, and S4 of the semiconductor wafer shown can have point indices between 1 and 4.

[0014] To measure overlay error for tool-induced displacement measurement, it is necessary to acquire images of the overlay marks. To acquire these images, the "measurement focus" at the corresponding point needs to be found. The "measurement focus" is the focal point used to obtain the optimal overlay mark image and may differ from the "standard focus" found using the autofocus system. Finding the "measurement focus" is relatively time-consuming. Therefore, a method is employed where a "reference signal value" is pre-acquired as the signal value from the autofocus system in the "standard focus" state, and then the objective lens is adjusted so that the signal value from the autofocus system matches the "reference signal value" before acquiring the overlay mark image.

[0015] Previously, the "reference signal value" found at a specific point in the unrotated state of the wafer was directly used to measure overlay error in a 180-degree rotated state. However, with the miniaturization and integration of semiconductor devices, the overlay marks have become smaller, leading to the problem that the area illuminated by the autofocus device may be larger than the size of the overlay marks. When the illumination deviates from the overlay marks and illuminates other surrounding overlay marks or scribe line boundaries, the possibility of signal distortion from the autofocus device increases. In addition, since the surrounding environment differs between the unrotated state and the 180-degree rotated state, the tool-induced displacement value measured by conventional methods may also be distorted. Therefore, if the tool-induced displacement value measured by conventional methods is used to correct the measured overlay error value, inaccurate overlay error values ​​may be obtained.

[0016] Figure 4 This is a diagram showing the overprinted markings and their surroundings in the unrotated state and the state after a 180-degree rotation. Figure 4 (a) shows the unrotated state. Figure 4 (b) shows the state in which the wafer is rotated 180 degrees. Figure 4 As shown, line L, which is located above the overlay mark OM in the unrotated state, is located below the overlay mark OM in the 180-degree rotation state. Furthermore, the laser beam LB, which serves as illumination for the autofocus device, extends beyond the overlay mark OM and illuminates the surrounding lines L. Therefore, reflected light from the surrounding lines L is also transmitted to the autofocus device.

[0017] Figure 5 It is a graph showing the distribution of the overlay error values ​​between points on the same wafer measured using conventional methods in two different overlay measurement devices. Figure 5 The illustration is based on a wafer with 25 points per field. Figure 5 In the chart, the X-axis represents the point index. The Y-axis represents the difference between the overlay error values ​​obtained in the two devices. The distribution of Y values ​​is the distribution among points with the same point index located in different fields. (See illustration.) Figure 5The overprinting error value used is the value obtained by subtracting the overprinting error value in the 180-degree rotation state from the overprinting error value in the unrotated state and then dividing by 2, rather than the ordinary overprinting error value.

[0018] exist Figure 5 In the image, the points within the frame (points 2, 3, 7, 8, and 9) represent points whose surrounding environment differs significantly between their unrotated and 180-degree rotated states. Figure 5 It can be seen that if the previous method is used, the difference in overprinting error values ​​of these points exhibits a different distribution than that of other points. It can be considered that the closer the average difference of points with the same index is to 0, the smaller the dispersion of the difference of points with the same index, and the more similar the distribution of points with different indices, the more accurate the overprinting error measurement can be achieved.

[0019] Existing technical documents

[0020] Patent Document 1: Japanese Patent Publication 2020-112807

[0021] Patent Document 2: Korean Patent Publication 10-2001-0092740

[0022] Patent Document 3: Korean Patent 10-2236184

[0023] Patent Document 4: Korean Patent 10-2524462

[0024] Patent Document 5: Korean Patent 10-1869573 Summary of the Invention

[0025] Technical issues

[0026] The present invention aims to improve the above-mentioned problems and provides an overlay measuring device that can improve the distortion caused by tool-induced displacement due to the area illuminated by the illumination used by the autofocus device being larger than the size of the overlay mark.

[0027] In addition, another objective is to provide a focus control method and a focus control program for a tool-induced displacement measurement device for overlay measurement.

[0028] Technical solution

[0029] To achieve the above objectives, the present invention provides a focus control method for an overlay measurement apparatus used for tool-induced displacement measurement. The focus control method includes: acquiring a first signal as a signal from an autofocus device when focusing on a corresponding point at each point in the reference field of a reference wafer in its unrotated state; acquiring a second signal as a signal from the autofocus device when focusing on a corresponding point at each point in the reference field after rotating the reference wafer 180 degrees; matching and storing the first and second signals with the corresponding points; placing the measurement target point of the target wafer within the field of view of the overlay measurement apparatus; and focusing based on the first signal matched with the measurement target point when the target wafer is in its unrotated state, and focusing based on the second signal matched with the measurement target point when the target wafer is rotated 180 degrees.

[0030] Furthermore, in the focus control method of the provided overlay measuring device, the autofocus device is a phase difference detection autofocus system, and the first signal and the second signal are signals based on the phase difference.

[0031] Furthermore, in the focus control method of the provided overlay measurement apparatus, the measurement target point is the reference field of the reference wafer or a point in a field different from the reference field.

[0032] Furthermore, in the focus control method of the provided overlay measurement apparatus, the measurement target wafer is the reference wafer or other wafers belonging to the same batch (Lot) as the reference wafer.

[0033] Furthermore, in the focus control method of the provided overlay measurement apparatus, the rotation of the measurement target wafer is confirmed by the position of the flat zone or notch of the wafer.

[0034] Furthermore, in the focus control method of the provided overlay measurement device, the first signal that matches the measurement object point is the first signal obtained from a point in the reference field that is at the same position as the measurement object point in the field.

[0035] Furthermore, the present invention provides an overlay measurement apparatus, comprising: an objective lens; a lens focusing actuator configured to move the objective lens to adjust the distance between the wafer and the objective lens; an autofocus device that outputs a signal corresponding to the distance between the objective lens and the wafer; and a controller communicatively coupled to the lens focusing actuator and the autofocus device.

[0036] The controller includes a memory storing instructions and a processor configured to execute the instructions, which cause the processor to perform the following steps: acquiring a first signal as a signal from the autofocus device when focusing on the corresponding point at each point of the reference field of the reference wafer in its unrotated state; acquiring a second signal as a signal from the autofocus device when focusing on the corresponding point at each point of the reference field after rotating the reference wafer by 180 degrees; matching and storing the first signal and the second signal with the corresponding point; placing the measurement target point of the measurement target wafer within the field of view of the overlay measurement device; and moving the objective lens to focus according to the first signal matching the measurement target point when the measurement target wafer is in its unrotated state, and moving the objective lens to focus according to the second signal matching the measurement target point when the measurement target wafer is in its 180-degree rotated state.

[0037] Furthermore, the present invention provides a program for controlling the focus of an overlay measurement apparatus, which is stored in a storage medium for executing a method of controlling the focus of the overlay measurement apparatus using a computing device. The program for controlling the focus of the overlay measurement apparatus causes the computing device to perform the following steps: acquiring a first signal as a signal from an autofocus device when focusing on a corresponding point at each point in the reference field of a reference wafer in its unrotated state; acquiring a second signal as a signal from the autofocus device when focusing on a corresponding point at each point in the reference field after rotating the reference wafer by 180 degrees; matching and storing the first signal and the second signal with the corresponding points; placing the measurement target point of the measurement target wafer within the field of view of the overlay measurement apparatus; focusing based on the first signal matched with the measurement target point when the measurement target wafer is in its unrotated state, and focusing based on the second signal matched with the measurement target point when the measurement target wafer is rotated by 180 degrees.

[0038] The effects of the invention

[0039] According to the present invention, the distortion of tool-induced displacement caused by the area illuminated by the illumination used by the autofocus device being larger than the size of the overlay mark is improved, thereby obtaining a more accurate tool-induced displacement value.

[0040] When such tools are used to induce displacement values ​​to correct overlay errors, overlay errors can be measured more accurately even in wafers with small overlay marks. Attached Figure Description

[0041] Figure 1 This is a plan view of an example of an engraved mark.

[0042] Figure 2 Showing from Figure 1 The signal acquired in one working area of ​​the overprinted mark shown.

[0043] Figure 3 This is a diagram showing an example of a wafer.

[0044] Figure 4 It is a diagram showing the overprinted markings and surrounding environment in the unrotated state and the 180-degree rotated state.

[0045] Figure 5 It is a graph showing the distribution of the overlay error values ​​between points on the same wafer measured using conventional methods in two different overlay measurement devices.

[0046] Figure 6 This is a schematic diagram of an overlay measuring device according to an embodiment of the present invention.

[0047] Figure 7 This is a sequence diagram of a focus control method for an overlay measuring device for tool-induced displacement measurement according to an embodiment of the present invention.

[0048] Figure 8 An example of a table storing a first signal and a second signal is shown.

[0049] Figure 9 This is a graph showing the distribution of the overlay error values ​​between points on the same wafer measured in two different overlay measurement devices using the focus control method of the present invention. Detailed Implementation

[0050] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, embodiments of the present invention can be modified in many other ways, and the scope of the present invention should not be construed as limited to the embodiments detailed below. The embodiments of the present invention are provided to provide a more complete explanation of the invention to those skilled in the art. Therefore, for the sake of clarity, the shapes of elements in the figures are exaggerated, and elements indicated by the same symbols on the drawings refer to the same elements.

[0051] Figure 6 This is a schematic diagram of an overlay measuring device according to an embodiment of the present invention. Figure 6As shown, the overlay measurement apparatus 100 includes: a stage 10 supporting a semiconductor wafer; an illumination optical system 20 illuminating overlay marks on the semiconductor wafer W; an imaging optical system 30 focusing reflected light from the overlay marks to image the overlay marks; an image detector 40 acquiring the overlay mark image imaged by the imaging optical system 30; an autofocus device 50; and a controller 60.

[0052] The overlay measuring device 100 is used to measure the overlay error between multiple consecutive pattern layers.

[0053] The stage 10 can be moved in mutually orthogonal X and Y directions by a horizontal drive unit. The stage 10 serves to support the semiconductor wafer W and move it horizontally. The stage 10 may be equipped with a vacuum chuck for fixing the semiconductor wafer W.

[0054] The illumination optical system 20 can be constructed using a variety of optical elements. For example, the illumination optical system 20 may include an illumination source 21, a beam splitter 23, and an objective lens 25. In addition, it may further include other optical elements such as lenses or apertures.

[0055] The illumination source 21 serves to generate illumination for the overlay markings. The illumination source 21 may include a light source capable of generating a wide band of light and a variable optical filter capable of adjusting the band of transmitted light. A laser diode or a light-emitting diode can be used as the light source. The illumination source 21 can adjust the band of light from the light source by combining optical filters, thereby generating illumination of multiple bands.

[0056] The beam splitter 23 is positioned between the illumination source 21 and the objective lens 25, and serves to transmit the illumination from the illumination source 21 to the objective lens 25.

[0057] Objective lens 25 serves to focus illumination onto the measurement position on the surface of semiconductor wafer W and collect reflected light from the measurement position. Objective lens 25 is mounted on lens focusing actuator 27. Lens focusing actuator 27 is used to adjust the distance between objective lens 25 and semiconductor wafer W. Focus control is achieved by moving objective lens 25 in the Z direction.

[0058] The imaging optical system 30 can be constructed using a variety of optical elements. For example, the imaging optical system 30 may include a hot or cold mirror 31 and a barrel lens 33. In addition, the imaging optical system 30 may use the objective lens 25 and beam splitter 23 of the illumination optical system 20. Furthermore, it may also include other optical elements such as lenses or apertures.

[0059] The hot or cold mirror 31 serves to prevent the illumination used by the autofocus device 50 from being directed towards the image detector 40. The hot mirror has high transmittance for short-wavelength light but reflects long-wavelength light. Conversely, the cold mirror has high transmittance for long-wavelength light but reflects short-wavelength light. When the illumination used by the autofocus device 50 is of a shorter wavelength than the image acquisition illumination, a cold mirror is used to reflect the reflected light caused by the illumination used by the autofocus device 50 in the direction of the autofocus device 50. Conversely, when the illumination used by the autofocus device 50 is of a longer wavelength than the image acquisition illumination, a hot mirror is used to reflect the reflected light caused by the illumination used by the autofocus device 50 in the direction of the autofocus device 50.

[0060] The reflected light collected by the objective lens 25 passes through the beam splitter 23 and is focused onto the image detector 40 by the lens barrel 33.

[0061] The image detector 40 serves to receive reflected light from the overlay marks caused by illumination and generate an image of the overlay marks. The image detector 40 can be a CCD (Charge-Coupled Device) camera or a CMOS (Complementary Metal-Oxide Semiconductor) camera. The image detector 40 can utilize an imaging element equipped with RGB (Red, Green, Blue) color filters, or it can utilize a monochrome imaging element.

[0062] The autofocus device 50 serves to provide information about the Z-direction position of the wafer surface w required for focusing on the object being measured. For example, the autofocus device 50 provides a signal corresponding to the distance between the objective lens 25 and the wafer surface w. Various types of autofocus systems can be used as the autofocus device 50. For example, phase-difference detection autofocus systems, contrast-sensing autofocus systems, hybrid autofocus systems, etc., can be used.

[0063] The phase difference detection autofocus system can determine the direction and distance that the objective lens 25 should move by using two or more sensors to sense the phase difference of the light entering the overlay measurement device 100 from the wafer w, which is the subject of the photograph.

[0064] A contrast-sensing autofocus system analyzes the contrast between bright and dark areas of an image to determine the focus point. This system determines the image focus when the contrast is maximized.

[0065] The hybrid autofocus system obtains the approximate focus distance through contrast sensing and then fine-tunes the focus position through phase difference detection.

[0066] The controller 60 is configured to communicate with the lens focusing 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, fixed storage device (ROM), storage device such as a hard disk or SSD, and wired or wireless communication devices. It also includes programs such as firmware or software stored on storage media such as memory, fixed storage device, or storage device.

[0067] As a controller 60, it can be used with computing devices such as MCUs (Micro controller units), desktop computers, laptops, smartphones, and smart tablets.

[0068] The controller 60 can cause the processor to execute the following commands via program instructions: Figure 7 The steps.

[0069] Figure 7 This is a sequence diagram of a focus control method for an overlay measuring device for tool-induced displacement measurement according to an embodiment of the present invention.

[0070] like Figure 7 As shown, the controller 60 performs step S1, which involves acquiring a first signal from the autofocus device as a signal when focusing on the corresponding point at each point of the reference field of the reference wafer in its unrotated state.

[0071] A reference wafer is one of several wafers belonging to the same lot. A reference wafer comprises multiple fields. Each field contains multiple (e.g., 25) dots. Overlay marks are located at these dots. The reference field is typically positioned at the center of the wafer.

[0072] In this step, a first signal is acquired at each point within the reference field as a signal for the autofocus device 50 when focusing on the overlay mark at the corresponding point. If a phase difference detection autofocus system is used as the autofocus device 50, the phase value output by the phase difference detection autofocus system can be the first signal when aligned with the focus applied during the acquisition of the overlay mark image for overlay error measurement, i.e., the "measurement focus".

[0073] In a typical imaging system, the focal point found by the autofocus device 50 is the "measurement focal point." However, since the overlay marks include overlay structures formed together with different pattern layers, the "measurement focal point" may lie between the overlay structures formed in the previous pattern layer and the overlay structures formed in the current pattern layer. In particular, when the height difference between the overlay structures is large, the difference between the focal point found by the autofocus device 50 and the "measurement focal point" may be significant. The "measurement focal point" can be found by evaluating the quality of the acquired overlay mark image using various quality indicators.

[0074] If a phase difference detection autofocus system is used as the autofocus device 50, a phase difference of 0 can be considered as focusing in a normal imaging system, but for overlay marks, focus ("measured focus") alignment may be achieved when the phase difference is not 0.

[0075] After acquiring the first signal at one point, the Pattern Recognition Unit (PRU) is used to center the next point in the field of view of the overlay measuring device 100. Then, the same method is used to acquire the first signal at the corresponding point.

[0076] This process is repeated until a first signal is acquired at all measurement points within the reference field. Depending on the type of patterned layers with overlaid marks, the height difference, etc., the first signal may vary from point to point.

[0077] Next, the controller 60 performs step S2, which involves acquiring a second signal from the autofocus device 50 at each point in the reference field after rotating the reference wafer by 180 degrees, as a signal when focusing on the corresponding point.

[0078] In this step, the stage on which the reference wafer is placed is first rotated 180 degrees.

[0079] Then, a second signal is acquired as a signal of the autofocus device 50 when focusing on the overlay mark at the corresponding point in the reference field used in step S1.

[0080] Ideally, the second signal for the overlay marks at the same location should be consistent with the first signal. However, in reality, the second signal may differ from the first signal. For example, when the size of the laser line used as illumination by the autofocus device 50 is larger than the size of the overlay mark, the laser may extend beyond the overlay mark of the measurement target location and also illuminate other surrounding overlay marks, patterns, etc. 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 wafer's rotation angle.

[0081] For a point located at the center of the reference field, the first signal and the second signal may be similar. However, for points such as those at the top or bottom of the reference field, where the surrounding environment of the marking changes significantly with the rotation angle, the difference between the second signal and the first signal may be very large.

[0082] This step is performed in the same manner as step S1.

[0083] Next, the controller 60 executes step S3, which matches and stores the first signal and the second signal with the corresponding points.

[0084] For example, such as Figure 8 As shown, the information can be stored in the memory or other storage device of the controller 60 in a table format, including formula ID, overlay mark ID, point index, first signal, second signal, etc. The table stores the first and second signals of all points within the reference field.

[0085] Next, the controller 60 executes step S4, which places the measurement target point of the measurement target wafer within the field of view of the overlay measurement device 100.

[0086] In this step, the controller 60 can move the wafer by moving the plane of the stage 10 supporting the wafer to be measured. The wafer to be measured can be a reference wafer or another wafer belonging to the same batch as the reference wafer.

[0087] This step may include a global alignment step and a point alignment step. The controller 60 uses a pattern recognition unit to ensure that the overlay marks of the measurement object points are within the field of view of the overlay measuring device 100.

[0088] The measurement point can be the reference field or other field point of the reference wafer used to acquire the first and second signals. Alternatively, it can be the field point of other wafers from the same batch manufactured using the same process.

[0089] If the point indices are the same, then even for points in other fields of the same wafer or in fields belonging to other wafers in the same batch, the first and second signals will be almost identical. Therefore, the first and second signal information obtained in the reference field can be applied to points in other fields of the same wafer and in fields of other wafers in the same batch.

[0090] Next, the controller 60 executes step S5, which involves moving the objective lens 25 to focus based on a first signal matching the position of the measurement object when the wafer being measured is in a non-rotating state, and moving the objective lens to focus based on a second signal matching the position of the measurement object when the wafer being measured is in a 180-degree rotating state.

[0091] The controller 60 determines whether the wafer to be measured, for which tool-induced displacement measurement is required, is in a static state or a 180-degree rotated state. The controller 60 may obtain the rotation state of the wafer to be measured, for example, by using a proximity sensor or similar means to confirm the position of the flat zone or notch of the wafer to be measured.

[0092] If the wafer being measured is in a stationary state, the controller 60 moves the objective lens 25 to focus using a first signal stored in a table that matches the point index and the corresponding measurement point. If the wafer being measured is rotated 180 degrees, the objective lens 25 is moved to focus using a second signal stored in a table.

[0093] The controller 60 can move the objective lens 25 until the signal output by the autofocus device 50 matches the first signal (or the second signal if it is in a 180-degree rotation state), thereby achieving focus. The controller 60 can adjust the Z-axis position of the objective lens 25 by controlling the lens focusing actuator 27.

[0094] After the objective lens 25 has moved, the illumination optical system 20 can be used to illuminate the measurement object point, and the reflected light from the overlay mark can be gathered by the imaging optical system 30 to image the overlay mark image onto the image detector 40, thereby obtaining the overlay mark image.

[0095] The overlay error in the X and Y directions was measured using overlay mark images acquired in the unrotated state. Then, the overlay error in the X and Y directions was measured again using overlay mark images acquired from the same points in the same manner after a 180-degree rotation.

[0096] The tool-induced displacement in the X direction of the corresponding overlay mark (point) can be, for example, the average of the sum of the X-direction overlay error in the unrotated state and the X-direction overlay error in the 180-degree rotated state. Similarly, the tool-induced displacement in the Y direction can be the average of the sum of the Y-direction overlay error in the unrotated state and the Y-direction overlay error in the 180-degree rotated state. Ideally, both the X-direction and Y-direction tool-induced displacements are zero.

[0097] The X-direction tool-induced displacement and Y-direction tool-induced displacement can be used to correct the overlay error value measured at the corresponding point.

[0098] Figure 9 This is a graph showing the distribution of the overlay error values ​​between points on the same wafer measured using the focus control method of the present invention in two different overlay measurement devices. Figure 9 In the chart, the X-axis represents the point index, and the Y-axis represents the difference in overlay error values ​​between the overlay measuring devices. (Similar to...) Figure 5 This shows the distribution of overlay error values ​​measured at points with the same index in multiple fields on a wafer.

[0099] like Figure 9As shown, using the focus control method of the present invention, the differences in overlay error values ​​between points with different point indices exhibit a similar distribution. That is, the deviation of each point caused by the distortion due to the illumination of the autofocus device is reduced.

[0100] The embodiments described above are merely preferred embodiments of the present invention. The scope of the present invention is not limited to the described embodiments. Within the scope of the technical concept and claims of the present invention, those skilled in the art will be able to make various changes, modifications or substitutions, and such embodiments should be understood to fall within the scope of the present invention.

[0101] Figure Labels

[0102] w: wafer, 10: stage, 20: illumination optical system, 30: imaging optical system, 40: image detector, 50: autofocus device, 60: controller.

Claims

1. A focus control method for an overlay measuring device, the overlay measuring device being used for tool-induced displacement measurement, characterized in that the focus control method of the overlay measuring device comprises: The step of acquiring a first signal as a signal from an autofocus device when focusing on a corresponding point at each point of the reference field of a reference wafer in an unrotated state, wherein the illumination of the autofocus device is an illumination that is longer than the overlay mark formed on the point. The step of acquiring a second signal as a signal from the autofocus device when focusing on the corresponding point at each point of the reference field after rotating the reference wafer by 180 degrees, wherein the illumination of the autofocus device is an illumination that is longer than the overlay mark formed on the point. The step of matching and storing the first signal and the second signal with the corresponding points; The step of placing the measurement point of the wafer being measured within the field of view of the overlay measurement device; as well as When the wafer being measured is in a non-rotating state, focusing is performed based on the first signal matching the position of the measurement object; when the wafer being measured is in a 180-degree rotation state, focusing is performed based on the second signal matching the position of the measurement object.

2. The focus control method of the overlay measuring device according to claim 1, characterized in that, 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. The focus control method of the overlay measuring device according to claim 1, characterized in that, The measurement point is the reference field of the reference wafer or a field different from the reference field.

4. The focus control method of the overlay measuring device according to claim 1, characterized in that, The wafer being measured is either the reference wafer or another wafer belonging to the same batch as the reference wafer.

5. The focus control method of the overlay measuring device according to claim 1, characterized in that, The location of the flat area or notch on the wafer is used to confirm whether the wafer being measured is rotating.

6. The focus control method of the overlay measuring device according to claim 1, characterized in that, The first signal that matches the measurement object point is the first signal obtained from a point in the reference field that is at the same position as the measurement object point in the field.

7. A measuring device for overlay measurement, characterized in that, include: Objective lens; A lens focusing actuator is configured to move the objective lens to adjust the distance between the wafer and the objective lens; An autofocus device that outputs a signal corresponding to the distance between the objective lens and the wafer; as well as A controller, which is communicatively integrated with the lens focusing actuator and the autofocus device. The controller includes a memory storing instructions and a processor configured to execute the instructions, which cause the processor to perform the following steps: The step of acquiring a first signal as a signal from the autofocus device when focusing on the corresponding point at each point of the reference field of the reference wafer in its unrotated state, wherein the illumination of the autofocus device is an illumination that is longer than the overlay mark formed on the point. The step of acquiring a second signal as a signal from the autofocus device when focusing on the corresponding point at each point of the reference field after rotating the reference wafer by 180 degrees, wherein the illumination of the autofocus device is an illumination that is longer than the overlay mark formed on the point. The step of matching and storing the first signal and the second signal with the corresponding points; The step of placing the measurement point of the wafer being measured within the field of view of the overlay measurement device; as well as When the wafer being measured is in a non-rotating state, the objective lens is moved to focus according to the first signal matching the position of the measurement object. When the wafer being measured is in a 180-degree rotation state, the objective lens is moved to focus according to the second signal matching the position of the measurement object.

8. A program for controlling the focal point of an overlay measuring apparatus, stored in a storage medium for executing a method of controlling the focal point of the overlay measuring apparatus using a computing device, the program for controlling the focal point of the overlay measuring apparatus being characterized in that the computing device performs the following steps: The step of acquiring a first signal as a signal from an autofocus device when focusing on a corresponding point at each point of the reference field of a reference wafer in an unrotated state, wherein the illumination of the autofocus device is an illumination that is longer than the overlay mark formed on the point. The step of acquiring a second signal as a signal from the autofocus device when focusing on the corresponding point at each point of the reference field after rotating the reference wafer by 180 degrees, wherein the illumination of the autofocus device is an illumination that is longer than the overlay mark formed on the point. The step of matching and storing the first signal and the second signal with the corresponding points; The step of placing the measurement point of the wafer being measured within the field of view of the overlay measurement device; as well as When the wafer being measured is in a non-rotating state, focusing is performed based on the first signal matching the position of the measurement object; when the wafer being measured is in a 180-degree rotation state, focusing is performed based on the second signal matching the position of the measurement object.

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