Overlay measurement device and method for setting overlay measurement device

Abstract

The present invention relates to an overlay measurement device and a method for setting the overlay measurement device. The present invention provides a method for setting an overlay measurement device for measuring an error between a first overlay mark and a second overlay mark which are a pair of overlay marks respectively formed on different layers of a wafer, wherein: a difference value (D) between a temporary measurement focus position and a reference focus position is obtained at reference measurement sites of the wafer; the focus position of an image acquisition device is adjusted at multiple measurement sites on the basis of the D value, and then a graphs of the change in signal is obtained from an auto-focusing detector while moving the position of an optical adjustment lens; and the optical adjustment lens is moved to a reference position having the smallest dispersion for each measurement site of the signal from the auto-focusing detector according to the position of the optical adjustment lens.

Description

Overlay measuring device and method of setting up the overlay measuring device

[0001] The present invention relates to an overlay measuring device and a setting method of the overlay measuring device.

[0002] Technological advancements are driving the shrinking size of semiconductor devices and increasing the density of integrated circuits. To meet these demands, various conditions must be met, and overlay tolerance is one of the key indicators.

[0003] Semiconductor devices are manufactured through numerous manufacturing processes. Forming an integrated circuit on a wafer requires numerous manufacturing processes to ensure the desired circuit structures and elements are sequentially formed at specific locations. The manufacturing process sequentially creates patterned layers on the wafer. Through these repeated stacking processes, electrically active patterns within the integrated circuit are created. If the individual structures are not aligned within the tolerances allowed by the production process, interference between the electrically active patterns can occur, potentially affecting the performance and reliability of the manufactured circuit. Overlay measurement tools are used to measure and verify alignment errors between these layers.

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

[0005] Hereinafter, a method for measuring the overlay of two layers using a Box in Box (BIB) overlay mark is briefly described. First, as illustrated in FIGS. 1 and 2, a first overlay mark (OM1), which is generally box-shaped, and a second overlay mark (OM2), which is generally box-shaped and smaller than the first overlay mark (1), are formed on two consecutive layers, respectively. Then, images of the first overlay mark (OM1) and the second overlay mark (OM2) are acquired at once. Next, as illustrated in FIG. 3, a waveform representing the change in intensity by position is acquired, and the center value (C1) of the first overlay mark (OM1) and the center value (C2) of the second overlay mark (OM2) are acquired, respectively. Then, by comparing these, the overlay error between the two layers is measured.

[0006] If the height difference between the two layers is not significant, the autofocus sensor can be used to automatically adjust the focus, and then a combined image of the first overlay mark (OM1) and the second overlay mark (OM2) can be acquired simultaneously. The standard focus found using the autofocus sensor may not be the optimal focus for acquiring the combined image, but this does not pose a significant problem if the height difference between the two layers is not significant.

[0007] However, with the advancement of semiconductor processing technology, there is now a need to accurately measure overlay errors between layers with large height differences and different optical properties. This presents a problem: the difference between the standard focus obtained using an autofocus sensor and the measured focus for more accurate measurements can be significant. For example, the standard focus obtained by an autofocus sensor may be located above the current layer, while the measured focus may be located between the previous layer and the current layer.

[0008] The position of the measurement focus takes a long time to find because it is found by comparing the contrast of the overlay mark images after acquiring multiple overlay mark images for each focus position using the optical system used to acquire the overlay mark images.

[0009] Ultimately, when measuring the overlay error between pattern layers with a large height difference, there is a problem that the overlay error cannot be accurately measured using an image acquired at a standard focus because the first overlay mark formed on the previous layer is not clear in the alignment image, and there is a problem that it takes a relatively long time to use an image acquired at a measurement focus.

[0010] In order to solve the problem of difficulty in accurately measuring the overlay error between pattern layers with a large height difference, as shown in FIGS. 4 and 5, a double-shot method was also used in which a waveform representing the change in intensity by position of a signal obtained after focusing on a first overlay mark (OM1) is obtained to obtain the center value (C1) of the first overlay mark (OM1), and a waveform representing the change in intensity by position of a signal obtained after focusing on a second overlay mark (OM2) is obtained to obtain the center value (C2) of the second overlay mark (OM2), thereby measuring the overlay error between the two layers.

[0011] However, this method had the problem that the inspection time was longer because the measurement focus position had to be found twice since two shots had to be taken each time to measure the overlay error.

[0012] To improve these problems, Korean Patent No. 10-2524462, filed and registered by the applicant, discloses a method for quickly measuring at other measurement sites by using the signal of an auto-focus device when the focus position of an overlay measurement device is at the measurement focus position as a reference.

[0013] However, when measuring overlay errors at multiple measurement sites on a wafer, there is a problem that there may be deviations between the overlay marks located at the measurement sites. In other words, there was a problem that the signal value of the autofocus device according to the focus position at each measurement site could be different. In this case, if the signal value of the autofocus device at the reference measurement site is used to adjust the focus position of the overlay measurement device at another measurement site, the focus may not be correct.

[0014] [Prior Art Literature]

[0015] Korean Patent Publication No. 2003-0054781 (July 2, 2003)

[0016] Korean Patent No. 10-0689709 (February 26, 2007)

[0017] Korean Patent No. 10-1564312 (October 23, 2015)

[0018] Korean Patent No. 10-2524462 (April 21, 2023)

[0019] The present invention is intended to improve the above-described problems, and aims to provide an overlay measurement device and a setting method of the overlay measurement device that minimize the impact of changes in the measurement site.

[0020] In order to achieve the above-described purpose, the present invention provides a setting method of an overlay measuring device that measures an error between a pair of first overlay marks and second overlay marks formed on different layers of a wafer.

[0021] Here, the overlay measuring device includes an auto-focus device having an image acquisition device configured to acquire alignment images of a first overlay mark and a second overlay mark that are paired at a plurality of focus positions; an optical adjustment lens arranged on a path of illumination light for automatic focus adjustment and configured to refract the illumination light; and an auto-focus detector configured to receive reflected light of the illumination light transmitted through the optical adjustment lens and generate a signal according to a focus position of the reflected light.

[0022] A method for setting an overlay measurement device comprises the steps of: a) using the image acquisition device to change the focus position at the reference measurement site of the wafer and acquiring a plurality of alignment images; b) using the plurality of alignment images to acquire a graph (G1) of a change in contrast value of a first overlay mark and a graph (G2) of a change in contrast value of a second overlay mark according to the focus position; c) finding a temporary measurement focus position based on the graph (G1) of a change in contrast value of the first overlay mark and the graph (G2) of a change in contrast value of the second overlay mark; d) selecting the graph (G1) of a change in contrast value of the first overlay mark or the graph (G2) of a change in contrast value of the second overlay mark as a reference graph, and determining a focus position where the selected reference graph has a maximum value as a reference focus position; e) obtaining a difference value (D) between the temporary measurement focus position and the reference focus position; f) after fixing the focus position of the image acquisition device to the temporary measurement focus position, moving the position of the optical adjustment lens in the optical axis direction, A step of obtaining a change graph of a signal from a focus detector, g) a step of moving to a next measurement site, h) a step of obtaining a plurality of alignment images while changing a focus position at a current measurement site using the image acquisition device, i) a step of obtaining a reference graph at a current measurement site using the plurality of alignment images at the current measurement site, j) a step of changing the focus position of the image acquisition device to a focus position at which a reference graph at the current measurement site has a maximum value and a corresponding measurement focus position based on the difference value (D), k) a step of obtaining a change graph of a signal from the auto-focus detector while moving the position of the optical adjustment lens, l) a step of repeating steps g) to k),m) a step of measuring the dispersion of the signal from the auto-focus detector according to the position of the optical adjustment lens for each measurement site, and finding a reference position having the smallest dispersion for each measurement site; and n) a step of moving the optical adjustment lens to the reference position.

[0023] In addition, the present invention provides a method for setting an overlay measurement device in which the temporary measurement focus position is a focus position where a graph (G1) of a change in contrast value of the first overlay mark and a graph (G2) of a change in contrast value of the second overlay mark intersect.

[0024] In addition, in the step j), the corresponding measurement focus position provides a setting method of an overlay measurement device that is a focus position moved by the difference value (D) from the focus position where the reference graph at the current measurement site has the maximum value.

[0025] In addition, in the step j), the corresponding measurement focus position is a setting method of an overlay measurement device that is a focus position moved by a distance obtained by multiplying the difference value (D) by a proportional constant (K) from the focus position at which the reference graph at the current measurement site has a maximum value.

[0026] In addition, the above proportional constant (K) provides a setting method of an overlay measurement device, which is a value obtained by dividing the interval (L2) between focus positions where the graphs of change in contrast values ​​of the first and second overlay marks at the current measurement site each have maximum values ​​by the interval (L1) between focus positions where the graphs of change in contrast values ​​of the first and second overlay marks at the reference measurement site each have maximum values.

[0027] In addition, a method for setting an overlay measurement device is provided, which further includes a step of determining a detector signal value for auto-focus, which serves as a reference for adjusting the focus position of the image acquisition device.

[0028] In addition, the method for setting an overlay measurement device is provided, wherein the signal value of the detector for auto-focus is a signal value from the detector for auto-focus when the optical adjustment lens is positioned at the reference position at the reference measurement site and the focus position of the image acquisition device is the temporary measurement focus position.

[0029] In addition, the method for setting an overlay measuring device is provided, wherein the signal value of the detector for auto-focus is an average value of signal values ​​from the detector for auto-focus obtained at measurement sites while the optical adjustment lens is positioned at the reference position and the focus position of the image measuring device is the temporary measurement focus position or the corresponding measurement focus position.

[0030] In addition, a method for setting an overlay measuring device in which the signal value from the detector for autofocus is a phase difference value is provided.

[0031] In addition, the dispersion diagram for each measurement site provides a setting method of an overlay measurement device that is a 3-sigma value of the signal value from the auto-focus detector obtained for each measurement site.

[0032] In addition, the present invention provides an overlay measuring device for measuring an error between pairs of first overlay marks and second overlay marks formed on different layers of a wafer, the overlay measuring device comprising: an image acquisition device configured to acquire alignment images of the pairs of first overlay marks and second overlay marks at a plurality of focus positions; an optical adjustment lens disposed on a path of illumination light for automatic focus adjustment and configured to refract the illumination light; and an auto-focus detector configured to receive reflected light of the illumination light transmitted through the optical adjustment lens and generate a signal according to a focus position of the reflected light; and a controller communicatively coupled to the image acquisition device and the auto-focus device.

[0033] Here, the controller includes a processor configured to execute a command, wherein the command causes the processor to perform the steps of: a) using the image acquisition device to change a focus position at a reference measurement site of the wafer and acquire a plurality of alignment images; b) using the plurality of alignment images to acquire a graph (G1) of a change in contrast value of a first overlay mark and a graph (G2) of a change in contrast value of a second overlay mark according to a focus position; c) finding a temporary measurement focus position based on the graph (G1) of a change in contrast value of the first overlay mark and the graph (G2) of a change in contrast value of the second overlay mark; d) selecting the graph (G1) of a change in contrast value of the first overlay mark or the graph (G2) of a change in contrast value of the second overlay mark as a reference graph, and determining a focus position where the selected reference graph has a maximum value as a reference focus position; e) obtaining a difference value (D) between the temporary measurement focus position and the reference focus position; and f) fixing the focus position of the image acquisition device to the temporary measurement focus position. After that, a step of obtaining a change graph of a signal from the auto-focus detector while moving the position of the optical adjustment lens in the direction of the optical axis, a step of moving to a next measurement site, a step of obtaining a plurality of alignment images while changing the focus position at the current measurement site using the image acquisition device, a step of obtaining a reference graph at the current measurement site using the plurality of alignment images at the current measurement site, a step of changing the focus position of the image acquisition device to a focus position at which the reference graph at the current measurement site has a maximum value and a corresponding measurement focus position based on the difference value (D), a step of obtaining a change graph of a signal from the auto-focus detector while moving the position of the optical adjustment lens, and a step of repeating steps g) to k).m) a step of measuring the dispersion of the signal from the auto-focus detector according to the position of the optical adjustment lens for each measurement site, and finding a reference position where the dispersion is the smallest for each measurement site; and n) a step of moving the optical adjustment lens to the reference position.

[0034] The overlay measurement device according to the present invention minimizes the impact of changes in measurement sites. Therefore, it can quickly and accurately measure overlay errors at multiple measurement sites.

[0035] Figure 1 is a plan view of an overlay mark.

[0036] Figure 2 is a side view of the overlay mark illustrated in Figure 1.

[0037] Figure 3 shows a waveform of change in intensity by position of a signal obtained from an image obtained by photographing the overlay mark illustrated in Figure 1.

[0038] FIG. 4 shows a waveform of change in intensity by position of a signal obtained from an image obtained while focusing on the first overlay mark of the overlay mark illustrated in FIG. 1.

[0039] FIG. 5 shows a waveform of change in intensity by position of a signal obtained from an image obtained while focusing on the second overlay mark of the overlay mark illustrated in FIG. 1.

[0040] FIG. 6 is a conceptual diagram of an overlay measuring device having an auto-focus device according to one embodiment of the present invention.

[0041] Figure 7 is a drawing for explaining the movement of a line beam according to the rotation of a cylinder lens.

[0042] Figure 8 is a flowchart of a method for setting an overlay measurement device according to one embodiment of the present invention.

[0043] Figure 9 is a drawing showing measurement sites on a semiconductor wafer as dots.

[0044] Figure 10 shows graphs showing changes in the contrast values ​​of the first overlay mark and the second overlay mark according to the focus position.

[0045] Figure 11 shows a graph of the change in signal from the detector for autofocus according to the position of the optical adjustment lens.

[0046] Figure 12 is a drawing for explaining a method for finding a corresponding measurement focus position.

[0047] Figure 13 is a drawing illustrating another method for finding a corresponding measurement focus position.

[0048] Figure 14 shows a graph of the change in signal from the autofocus detector according to the position of the optical adjustment lens at each measurement site.

[0049] Figure 15 is a graph showing the dispersion of signals from an autofocus detector according to the position of the optical adjustment lens.

[0050] 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.

[0051] Figure 6 is a conceptual diagram of an overlay measuring device equipped with an auto-focus device according to one embodiment of the present invention. The overlay measuring device is a device that measures the error between a first overlay mark and a second overlay mark formed on different layers of a wafer (w).

[0052] For example, as illustrated in FIGS. 1 and 2, the first overlay mark (OM1) may be an overlay mark formed on a previous layer, and the second overlay mark (OM2) may be an overlay mark formed on a current layer. The overlay marks are formed on a scribe lane while simultaneously forming a layer for forming a semiconductor device in a die area. For example, the first overlay mark (OM1) may be formed together with an insulating film pattern, and the second overlay mark (OM2) may be formed together with a photoresist pattern formed on the insulating film pattern.

[0053] In this case, the second overlay mark (OM2) is exposed to the outside, but the first overlay mark (OM1) is covered by a photoresist layer and is made of an oxide having different optical properties from the second overlay mark (OM2) made of a photoresist material. In addition, the first overlay mark (OM1) and the second overlay mark (OM2) have different heights.

[0054] Overlay marks can be used in a variety of forms, including box-in-box (see Figure 1) and AIM (Advanced Imaging Metrology) overlay marks.

[0055] As illustrated in FIG. 6, an overlay measuring device (1) according to one embodiment of the present invention includes an imaging system (10) and a controller (20) communicatively coupled to the imaging system (10).

[0056] The imaging system (10) largely includes an image acquisition device (100) and an autofocus device (200).

[0057] The image acquisition device (100) serves to acquire an image (hereinafter referred to as an 'alignment image', for example, the image of FIG. 1) in which a first overlay mark (OM1) and a second overlay mark (OM2) are displayed together at multiple focus positions.

[0058] An image acquisition device (100) comprises an image acquisition light source (111), a first beam splitter (113), an objective lens (115), and a first actuator (117) to irradiate image acquisition illumination light onto a measurement site of a wafer (W). The measurement site is an area in a scribe lane of the wafer (W) where a first overlay mark (OM1) and a second overlay mark (OM2) are formed. A single wafer (W) has a plurality of measurement sites. The overlay measurement device (1) measures an overlay error at the plurality of measurement sites.

[0059] A halogen lamp, a xenon lamp, a light-emitting diode, a supercontinent laser, etc. can be used as a light source (111) for image acquisition. The light source (111) for image acquisition can generate, for example, illumination light for image acquisition in the visible light range.

[0060] The first beam splitter (113) serves to reflect the image acquisition illumination light from the image acquisition light source (111) and guide it toward the objective lens (115). In addition, it transmits the reflected light collected by the objective lens (115).

[0061] The objective lens (115) focuses the beam reflected from the first beam splitter (113) onto the measurement site of the wafer (W) and collects the reflected light reflected from the measurement site. The objective lens (115) is installed on the first actuator (Actuator, 117).

[0062] The first actuator (117) adjusts the distance between the objective lens (115) and the wafer (W) to adjust the focus position of the image acquisition device (100).

[0063] In addition, the image acquisition device (100) is equipped with a hot mirror (121), a tube lens (123), and an image detector (130) to collect reflected light from a measurement site of a wafer (W) to obtain an alignment image.

[0064] The tube lens (123) serves to focus the reflected light passing through the first beam splitter (113) and the hot mirror (121) onto the image detector (130).

[0065] The hot mirror (121) reflects light having a longer wavelength than a reference wavelength and transmits light having a shorter wavelength than the reference wavelength. For example, the hot mirror (121) may reflect infrared light and transmit visible light, or reflect infrared light having a relatively longer wavelength and transmit infrared light having a relatively shorter wavelength. The hot mirror (121) may prevent long-wavelength light used in the height and tilt measurement system (200) from entering the image detector (130).

[0066] The image detector (130) may be a CCD or CMOS camera. The image acquisition device (100) acquires an alignment image using an electrical signal from the image detector (130). By analyzing this alignment image, the overlay error can be measured.

[0067] The autofocus device (200) generates a signal according to the distance between the objective lens (115) and the wafer (W). In other words, it generates a signal according to changes in the focus position of the image acquisition device (100). In addition, it can also use this signal to control the first actuator (117) to focus.

[0068] An autofocus device (200) comprises an autofocus light source (211) for irradiating autofocus illumination light onto a measurement site of a wafer (W), an optical adjustment lens (212) for refracting the illumination light from the light source (211), and a second beam splitter (213). In addition, a hot mirror (121), a first beam splitter (113), and an objective lens (115) of an image acquisition device (100) are also used as part of the autofocus device (200).

[0069] A laser diode or a light-emitting diode can be used as the auto-focus light source (211). The auto-focus light source (211) generates illumination light in the infrared region. The illumination light is refracted by an optical adjustment lens (212), then passes through a second beam splitter (213), and is reflected by a hot mirror (121). A plano-convex lens can be used as the optical adjustment lens (212). When a laser is used as the illumination light, it is preferable to use a polarizing beam splitter as the second beam splitter (213). This is because it can minimize the reduction in the amount of light during reflection and transmission.

[0070] And the illumination light reflected from the hot mirror (121) passes through the first beam splitter (113) and then enters the objective lens (115). The objective lens (115) focuses the illumination light on the measurement site of the wafer (W) and collects the reflected light reflected from the measurement site. The present invention can focus the illumination light for image acquisition and the illumination light for auto-focus using one objective lens (115) and collect the reflected light of these illumination lights.

[0071] In the present invention, infrared light having a different wavelength band from the image acquisition illumination light is used as the auto-focus illumination light, and the reflected light thereof is separated from each other using a hot mirror (121), thereby preventing the reflected light of the auto-focus illumination light from entering the image detector (130).

[0072] The reflected light of the auto-focus illumination light collected from the objective lens (115) passes through the first beam splitter (113) again and is then reflected from the hot mirror (121). Since infrared rays do not pass through the hot mirror (121), the reflected light in the infrared region does not enter the image detector (130).

[0073] The reflected light from the hot mirror (121) is reflected from the second beam splitter (213) toward the detector (230) for autofocus.

[0074] Various autofocus sensor modules can be used as the autofocus detector (230). For example, a phase-difference autofocus sensor module including a beam splitter, a microlens, and a pair of photodiodes can be used. Furthermore, a phase-difference autofocus sensor module including a focusing lens, a chopper wheel, and a bi-cell photodiode can also be used.

[0075] The autofocus detector (230) receives reflected light and generates a signal according to the distance between the objective lens (115) and the wafer (W).

[0076] The autofocus device (200) further includes a second actuator (217), a cylinder lens (215), and a cylinder lens holder (219).

[0077] The second actuator (217) adjusts the position of the optical adjustment lens (212) between the autofocus light source (211) and the cylinder lens (215). The second actuator (217) moves the optical adjustment lens (212) along the optical axis.

[0078] The cylinder lens (215) is placed between the optical adjustment lens (212) and the objective lens (115). Various cylinder lenses (215) having a rectangular, square, circular, or oval shape can be used as the cylinder lens (215). The cylinder lens (215) is a lens that focuses light on a line rather than a point. The cylinder lens (215) forms a line beam. Using a line beam has the advantage of increasing sensitivity due to optical aberration (astigmatism), thereby enabling more precise measurements. It is preferable that the line beam is formed so as not to be parallel to the lines forming the overlay mark. In addition, it is preferable that the line beam does not go beyond the overlay mark. This is because if the line beam goes beyond the overlay mark, it may be affected by structures located outside the overlay mark, such as other adjacent overlay marks.

[0079] The cylinder lens holder (219) serves to support the cylinder lens (215). In addition, the cylinder lens holder (219) also serves to rotate the cylinder lens (215) clockwise or counterclockwise about at least one rotation axis that is orthogonal to the optical axis of the cylinder lens (215). The rotation axis may include a first rotation axis and a second rotation axis that is orthogonal to the first rotation axis. When the cylinder lens (215) rotates, the line beam moves within the measurement site.

[0080] Fig. 7 is a drawing for explaining the movement of the line beam according to the rotation of the cylinder lens. Rotation of the cylinder lens (215) about the first rotation axis can move the position of the line beam (LB) illuminating the measurement site within the measurement site, for example, in a direction parallel to the first direction (Fig. 7 a, b). And rotation about the second rotation axis can move the line beam (LB) in a direction parallel to the second direction orthogonal to the first direction (Fig. 7 c, d). Therefore, the position of the line beam (LB) within the measurement site can be adjusted by adjusting the rotation angles of the cylinder lens about the first and second rotation axes.

[0081] The controller (20) is connected to the imaging system (10) in a wired or wireless manner. The controller (20) includes hardware such as a processor and memory, and software installed in the memory. The controller (20) can instruct the processor to perform the steps of FIG. 8 through software commands.

[0082] Hereinafter, a method for setting up an overlay measurement device according to an embodiment of the present invention will be described. Fig. 8 is a flowchart of a method for setting up an overlay measurement device according to an embodiment of the present invention.

[0083] First, a step (S1) of acquiring multiple alignment images by changing the focus position at the reference measurement site of the wafer (W) using an image acquisition device (100) is described.

[0084] Figure 9 is a drawing showing measurement sites on a semiconductor wafer as dots. As shown in Figure 9, there are multiple measurement sites on the semiconductor wafer (W).

[0085] At the measurement site, an overlay mark is formed, including a first overlay mark (OM1) and a second overlay mark (OM2) formed on different pattern layers, respectively.

[0086] The reference measurement site may be a reference measurement site among multiple measurement sites. For example, the reference measurement site may be a measurement site located at the center of a wafer (W).

[0087] In this step, the wafer (W) is moved so that the reference measurement site is positioned in the field of view of the image acquisition device (100). The wafer (W) can be moved by moving the XY stage of the image acquisition device (100) to which the wafer (W) is fixed.

[0088] Next, while changing the focus position of the image acquisition device (100), a plurality of alignment images are acquired. The alignment images display a first overlay mark (OM1) and a second overlay mark (OM2) together. The focus position can be changed by moving the objective lens (115) of the image acquisition device (100) in the optical axis direction to adjust the distance between the objective lens (115) and the wafer (W). At this time, the optical adjustment lens (212) of the autofocus device (200) is fixed to a predetermined origin.

[0089] Next, a step (S2) of obtaining a graph (G1) of change in contrast value of a first overlay mark (OM1) according to a focus position and a graph (G2) of change in contrast value of a second overlay mark (OM2) using multiple aligned images is described.

[0090] Figure 10 shows graphs (G1, G2) showing changes in the contrast values ​​of the first overlay mark (OM1) and the second overlay mark (OM2) according to the focus position.

[0091] As illustrated in FIG. 10, the contrast value of the first overlay mark (OM1) portion and the contrast value of the second overlay mark (OM2) portion included in the alignment image change depending on the focus position. At this time, since the first overlay mark (OM1) and the second overlay mark (OM2) have different heights and different materials, the graph (G1) of the change in the contrast value of the first overlay mark (OM1) portion and the graph (G2) of the change in the contrast value of the second overlay mark (OM2) portion in the alignment image have different shapes.

[0092] That is, since the first overlay mark (OM1) is formed together with the previous layer, in the graph (G1) of the change in contrast value by the first overlay mark (OM1), the contrast value has a maximum value at a low focus position. Since the second overlay mark (OM2) is formed together with the current side, in the graph (G2) of the change in contrast value by the second overlay mark (OM2), the contrast value has a maximum value at a relatively high focus position. Generally, the contrast value has a maximum value at a position that is in focus. This is because when the focus is on, the boundary between the object (overlay mark) and the background becomes clear, and the difference in brightness becomes larger.

[0093] Next, the temporary measurement focus position (F T ) is described in the step (S3).

[0094] As described above, since there is a height difference, the focus positions where the first overlay mark (OM1) is clearly captured and the focus positions where the second overlay mark (OM2) is clearly captured are different. However, since an overlay mark image (alignment image) including both the first overlay mark (OM1) and the second overlay mark (OM2) must be acquired with a single capture, a temporary measurement focus position (F) at which both the first overlay mark (OM1) and the second overlay mark (OM2) can be captured with a certain degree of clarity is required. T ) must be found.

[0095] Temporary measurement focus position (F T ) can be found, for example, between the focus position (F1) where the graph of change in contrast value (G1) by the first overlay mark (OM1) has a maximum value and the focus position (F2) where the graph of change in contrast value (G2) by the second overlay mark (OM2) has a maximum value.

[0096] For example, as shown in Fig. 10, the position where the graph of change in contrast value (G1) by the first overlay mark (OM1) and the graph of change in contrast value (G2) by the second overlay mark (OM2) intersect is called the temporary measurement focus position (F T ) can be determined.

[0097] Additionally, in another embodiment, a focus position having an average value of the maximum value of the change graph (G1) of the contrast value by the first overlay mark (OM1) and the maximum value of the change graph (G1) of the contrast value by the second overlay mark (OM2) may be set as a temporary measurement focus position.

[0098] In some cases, the temporary measurement focus position may be located outside the section between the focus position (F1) at which the graph of change in contrast value (G1) by the first overlay mark (OM1) has a maximum value and the focus position (F2) at which the graph of change in contrast value (G2) by the second overlay mark (OM2) has a maximum value.

[0099] Next, a step (S4) of selecting one of the graphs (G1) of change in contrast value by the first overlay mark (OM1) and the graph (G2) of change in contrast value by the second overlay mark (OM2) as a reference graph and setting the focus position where the reference graph has the maximum value as the reference focus position is described.

[0100] In this step, one of the focus position (F1) where the contrast value change graph (G1), which is the focus position focused on the first overlay mark (OM1), has the maximum value or the focus position (F2) where the contrast value change graph (G2) has the maximum value is set as the reference focus position. Hereinafter, a case will be described as an example in which the contrast value change graph (G1) by the first overlay mark (OM1) is the reference graph and the focus position (F1) where the contrast value change graph (G1) by the first overlay mark (OM1) has the maximum value is the reference focus position.

[0101] Next, the temporary measurement focus position (F T ) and the reference focus position.

[0102] In this step, as shown in Fig. 10, a temporary measurement focus position (F T ) can be obtained as the difference value (D) by subtracting the reference focus position.

[0103] Next, the focus position of the image acquisition device (100) is temporarily measured as the focus position (F T ) and then moving the position of the optical adjustment lens (212) in the direction of the optical axis, a step (S6) of obtaining a graph of changes in the signal from the auto-focus detector (230) is described.

[0104] In this step, first, the focus position of the image acquisition device (100) is set to a temporary measurement focus position (F T ) is fixed. Then, the position of the optical adjustment lens (212) of the auto-focus device (200) is moved in the direction of the optical axis. Then, the distance between the optical adjustment lens (212) and the light source (211) of the auto-focus device (200) is changed, and as a result, the focus position of the reflected light from the reference measurement site incident on the auto-focus detector (230) is changed, so that the signal from the auto-focus detector (230) changes.

[0105] For example, if the autofocus device (200) is a phase difference type autofocus device, as shown in FIG. 11, the phase difference value from the autofocus detector (230) changes according to the position on the optical axis of the optical adjustment lens (212).

[0106] Next, the step (S7) of moving to the next measurement site is described.

[0107] In this step, the wafer (W) is moved so that the next measurement site is positioned in the field of view of the image acquisition device (100). As described above, the wafer (W) can be moved by moving an XY stage or the like on which the wafer (W) is fixed.

[0108] Next, a step (S8) of changing the focus position at the current measurement site and acquiring multiple alignment images using an image acquisition device (100) is described.

[0109] In this step, multiple aligned images are acquired by changing the focus position in the same manner as in step S1. At this time, the optical adjustment lens (212) of the autofocus device (200) is positioned at the origin.

[0110] Next, a step (S9) of obtaining a reference graph at the current measurement site using multiple aligned images at the current measurement site is described.

[0111] In this step, among the graphs (G1`) of change in contrast value of the first overlay mark (OM1) at the current measurement site and the graphs (G2`) of change in contrast value of the second overlay mark (OM2), the graph corresponding to the graph selected as the reference graph at the reference measurement site is selected as the reference graph.

[0112] For example, as described above, if the graph (G1) of the change in the contrast value of the first overlay mark (OM1) at the reference measurement site is selected as the reference graph, the graph (G1`) of the change in the contrast value of the first overlay mark (OM1) is also selected as the reference graph at the current measurement site.

[0113] Ideally, the graphs of the change in contrast values ​​of the first and second overlay marks at the reference measurement site (G1, G2) and the graphs of the change in contrast values ​​of the first and second overlay marks at the current measurement site (G1`, G2`) should be identical. However, in reality, the graphs of the change in contrast values ​​differ from one measurement site to another due to errors in the process of forming the overlay mark or errors in measurement.

[0114] Next, the maximum value of the reference graph based on the focus position of the image acquisition device (100) and the corresponding measured focus position (F) based on the difference value (D) C ) is described.

[0115] In this step, the focus position of the image acquisition device (100) is set to a temporary measurement focus position (F) at the reference measurement site. T ) corresponding to the corresponding measurement focus position (F C ) is changed to .

[0116] For example, as shown in Fig. 12, a focus position that is separated by a difference value (D) from the reference focus position (F1` in Fig. 12) is referred to as a corresponding measurement focus position (F C ) can be selected. As can be seen in Fig. 12, the corresponding measurement focus position (F C ), the graphs (G1`, G2`) of the change in contrast values ​​of the first and second overlay marks at the current measurement site may not intersect each other.

[0117] Alternatively, as shown in Fig. 13, the focal point position is obtained by multiplying the difference value (D) by a proportional constant (K) that takes into account the difference between the reference measurement site and the current measurement site, and then the focal point position is obtained by the corresponding measurement focal point position (F). C ) can be selected.

[0118] For example, the value obtained by dividing the interval (L2) between the focus positions (F1`, F2`) where the graphs (G1`, G2`) of the change in contrast values ​​of the first and second overlay marks at the current measurement site each have maximum values ​​by the interval (L1) between the focus positions (F1, F2) where the graphs (G1, G2) of the change in contrast values ​​of the first and second overlay marks at the reference measurement site each have maximum values ​​can be used as the proportional constant (K).

[0119] In Fig. 13, the corresponding measurement focus position (F C ) can be calculated using the mathematical formula 1 below.

[0120]

[0121] Next, a step (S11) of obtaining a graph of changes in a signal from an auto-focus detector (230) while moving the position of an optical adjustment lens (212) is described.

[0122] In this step, the focus position of the image acquisition device (100) is determined by the corresponding measurement focus position (F) found in step S10. C ) is fixed to the autofocus device (200), and a graph of the change in the signal from the autofocus detector (230) is obtained while changing the position of the optical adjustment lens (212).

[0123] Next, steps S7 to S11 are repeated at other measurement sites (S12).

[0124] By repeating this process at other measurement sites, graphs of signal changes from multiple auto-focus detectors (230) can be obtained, as shown in Fig. 14. Fig. 14 illustrates a case where there are five measurement sites, but there may be six or more measurement sites.

[0125] Next, a step (S13) of measuring the dispersion of a signal from an auto-focus detector (230) according to the position of an optical adjustment lens (212) is described.

[0126] In this step, the dispersion of the signal from the auto-focus detector (230) for each measurement site according to the position of the optical adjustment lens (212) is measured. For example, a 3-sigma value can be used as the dispersion value. In the dispersion graph illustrated in Fig. 15, the dispersion is the lowest when the position of the optical adjustment lens (212) is 0.2 mm. This means that when the position of the optical adjustment lens (212) is 0.2 mm away from the origin, the signals from the auto-focus detector (230) measured at different measurement sites are densely clustered around the average value. In other words, this indicates that the data has low variability and high stability.

[0127] Next, the optical adjustment lens (212) is moved to the reference position where the dispersion is the smallest for each measurement site (S14).

[0128] In this step, the position of the optical adjustment lens (212) is moved to the reference position where the dispersion is the smallest for each measurement site. When acquiring an alignment image for measuring overlay errors at all measurement sites, the optical adjustment lens (212) is positioned at the reference position.

[0129] Next, an automatic detector signal value that serves as a reference for adjusting the focus position of the image acquisition device (100) is determined (S15).

[0130] In this step, the signal value of the autofocus detector (230) that can be used as a reference when determining the focus position of the image acquisition device (100) at the measurement sites is determined. The focus position of the image acquisition device (100) can be adjusted by adjusting the optical axis direction position of the objective lens (115).

[0131] For example, at the reference measurement site, the optical adjustment lens (212) is positioned at the reference position with the smallest dispersion, and the focus position of the image acquisition device (100) is positioned at the temporary measurement focus position (F T ) can be used as a reference value when determining the focus position of the image acquisition device (100) at each measurement site, based on the signal value (e.g., phase difference value) from the auto-focus detector (230).

[0132] In this case, when measuring at other measurement sites, the optical adjustment lens (212) can be fixed at a reference position, and the focus position of the image acquisition device (100) can be adjusted by adjusting the position of the objective lens (115) so that the signal value from the auto-focus detector (230) becomes the same as the reference value.

[0133] Alternatively, the optical adjustment lens (212) is positioned at the reference position, and the focus position of the image measuring device (100) is positioned at the temporary measurement focus position (F T ) or corresponding measurement focus position (F C ) may be used as a reference value by taking the average of the signal values ​​from the auto-focus detector (230) obtained from the measurement sites.

[0134] 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.

[0135] [Explanation of symbols]

[0136] OM1: First overlay mark

[0137] OM2: Second overlay mark

[0138] 1: Overlay measuring device

[0139] 20: Controller

[0140] 100: Image acquisition device

[0141] 111: Light source for image acquisition

[0142] 115: Objective lens

[0143] 117: First actuator

[0144] 121: Hot Mirror

[0145] 130: Image detector

[0146] 200: Autofocus device

[0147] 211: Light source for autofocus

[0148] 212: Optical adjustment lens

[0149] 215: Cylinder lens

[0150] 219: Cylinder lens holder

[0151] 217: Second actuator

[0152] 230: Detector for autofocus

Claims

1. A method for setting an overlay measuring device for measuring an error between a pair of first overlay marks and second overlay marks formed on different layers of a wafer, The above overlay measuring device, An image acquisition device configured to acquire alignment images of a first overlay mark and a second overlay mark that are paired at a plurality of focus positions; An autofocus device comprising an optical adjustment lens arranged on a path of illumination light for automatic focus control and configured to refract the illumination light, and an autofocus detector configured to receive reflected light of the illumination light transmitted through the optical adjustment lens and generate a signal according to a focus position of the reflected light. a) A step of acquiring multiple alignment images by changing the focus position at the reference measurement site of the wafer using the image acquisition device; b) A step of obtaining a graph (G1) of change in contrast value of a first overlay mark according to a focus position and a graph (G2) of change in contrast value of a second overlay mark using the plurality of aligned images, c) a step of finding a temporary measurement focus position based on a graph (G1) of change in contrast value of the first overlay mark and a graph (G2) of change in contrast value of the second overlay mark; d) a step of selecting a graph of change in contrast value of the first overlay mark (G1) or a graph of change in contrast value of the second overlay mark (G2) as a reference graph, and setting a focus position where the selected reference graph has a maximum value as a reference focus position; e) a step of obtaining a difference value (D) between the temporary measurement focus position and the reference focus position; f) a step of obtaining a graph of changes in a signal from the auto-focus detector while moving the position of the optical adjustment lens in the direction of the optical axis after fixing the focus position of the image acquisition device to the temporary measurement focus position; g) Steps to move to the next measurement site, and h) A step of acquiring multiple alignment images by changing the focus position at the current measurement site using the image acquisition device, i) a step of obtaining a reference graph at the current measurement site using the plurality of alignment images at the current measurement site, j) a step of changing the focus position of the image acquisition device to a focus position at which the reference graph at the current measurement site has a maximum value and a corresponding measurement focus position based on the difference value (D); k) A step of obtaining a graph of changes in a signal from the auto-focus detector while moving the position of the optical adjustment lens; l) a step of repeating steps g) to k), and m) A step of measuring the dispersion of the signal from the auto-focus detector according to the position of the optical adjustment lens at each measurement site, and finding a reference position with the smallest dispersion at each measurement site; n) A setting method of an overlay measuring device including a step of moving the optical adjustment lens to the reference position.

2. In paragraph 1, A setting method of an overlay measuring device, wherein the temporary measurement focus position is a focus position where a graph (G1) of a change in contrast value of the first overlay mark and a graph (G2) of a change in contrast value of the second overlay mark intersect.

3. In paragraph 1, In the above step j), The above corresponding measurement focus position is a setting method of an overlay measurement device in which the focus position is moved by the difference value (D) from the focus position at which the reference graph at the current measurement site has the maximum value.

4. In paragraph 1, In the above step j), The above corresponding measurement focus position is a setting method of an overlay measurement device in which the focus position is moved by a distance obtained by multiplying the proportional constant (K) by the difference value (D) from the focus position where the reference graph at the current measurement site has the maximum value.

5. In paragraph 4, The above proportional constant (K) is a setting method of an overlay measurement device, which is a value obtained by dividing the interval (L2) between focus positions at which the graphs of the change in contrast values ​​of the first and second overlay marks at the current measurement site each have a maximum value by the interval (L1) between focus positions at which the graphs of the change in contrast values ​​of the first and second overlay marks at the reference measurement site each have a maximum value.

6. In paragraph 1, A setting method of an overlay measurement device further comprising a step of determining a detector signal value for auto-focus that serves as a reference for adjusting the focus position of the image acquisition device.

7. In paragraph 6, The above autofocus detector signal values ​​are: A setting method of an overlay measurement device, wherein the optical adjustment lens is positioned at the reference position, and the focus position of the image acquisition device is the temporary measurement focus position, which is a signal value from the detector for autofocus.

8. In paragraph 6, The above autofocus detector signal values ​​are: A setting method of an overlay measuring device, wherein the optical adjustment lens is positioned at the reference position, and the focus position of the image measuring device is the temporary measurement focus position or the corresponding measurement focus position, which is an average value of signal values ​​from the auto-focus detector obtained at the measurement sites.

9. In paragraph 1, A method for setting an overlay measuring device in which the signal value from the above autofocus detector is a phase difference value.

10. In paragraph 1, The above measurement site-specific dispersion is a setting method of an overlay measurement device in which the 3-sigma value of the signal value from the auto-focus detector obtained for each measurement site is used.

11. An overlay measuring device for measuring an error between a pair of first overlay marks and a second overlay mark formed on different layers of a wafer, An image acquisition device configured to acquire alignment images of a first overlay mark and a second overlay mark that are paired at a plurality of focus positions; An autofocus device comprising an optical adjustment lens arranged on a path of illumination light for automatic focus control and configured to refract the illumination light, and an autofocus detector configured to receive reflected light of the illumination light transmitted through the optical adjustment lens and generate a signal according to the focus position of the reflected light; A controller communicatively coupled to the image acquisition device and the autofocus device, The controller comprises a processor configured to execute instructions, the instructions causing the processor to: a) A step of acquiring multiple alignment images by changing the focus position at the reference measurement site of the wafer using the image acquisition device; b) A step of obtaining a graph (G1) of change in contrast value of a first overlay mark according to a focus position and a graph (G2) of change in contrast value of a second overlay mark using the plurality of aligned images, c) a step of finding a temporary measurement focus position based on a graph (G1) of change in contrast value of the first overlay mark and a graph (G2) of change in contrast value of the second overlay mark; d) a step of selecting a graph of change in contrast value of the first overlay mark (G1) or a graph of change in contrast value of the second overlay mark (G2) as a reference graph, and setting a focus position where the selected reference graph has a maximum value as a reference focus position; e) a step of obtaining a difference value (D) between the temporary measurement focus position and the reference focus position; f) a step of obtaining a graph of changes in a signal from the auto-focus detector while moving the position of the optical adjustment lens in the direction of the optical axis after fixing the focus position of the image acquisition device to the temporary measurement focus position; g) Steps to move to the next measurement site, and h) A step of acquiring multiple alignment images by changing the focus position at the current measurement site using the image acquisition device, i) a step of obtaining a reference graph at the current measurement site using the plurality of alignment images at the current measurement site, j) a step of changing the focus position of the image acquisition device to a focus position at which the reference graph at the current measurement site has a maximum value and a corresponding measurement focus position based on the difference value (D); k) A step of obtaining a graph of changes in a signal from the auto-focus detector while moving the position of the optical adjustment lens; l) a step of repeating steps g) to k), and m) A step of measuring the dispersion of the signal from the auto-focus detector according to the position of the optical adjustment lens at each measurement site, and finding a reference position with the smallest dispersion at each measurement site; n) An overlay measuring device characterized in that it performs a step of moving the optical adjustment lens to the reference position.

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