Overlay measurement apparatus and method for controlling focus shift, and program storage medium therefor

Abstract

To provide an overlay measurement device controlling a focus movement, a method and a program storage medium.SOLUTION: An overlay measurement device 100 controlling a focus movement includes a processor 170 that controls the operation of a lens focus actuator 125 which operates an objective lens 120 and adjusts a distance to a wafer. The processor obtains a focus graph for each of two layers of a reference image, identifies a reference focus on the acquired focus graph, identifies a light-dark index for two layers of the acquired measured image on the basis of the identified reference focus when the measured image is acquired, identifies the focus corresponding to each of the identified light-dark indexes in each of the two layers of the reference image, calculates a difference between the reference focus and the identified focus, and moves the objective lens 120 to the focus corresponding to the measured image.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an overlay measurement apparatus and method for controlling focus movement, and a program storage medium therefor. [Background technology]

[0002] Typically, as technology advances, the size of the semiconductor devices that are to be measured on the wafer decreases, and the density of integrated circuits in the measurement equipment increases. To form integrated circuits on a wafer, a number of manufacturing steps must be performed to sequentially form the desired circuit structures and elements at specific locations. These manufacturing steps sequentially produce patterned layers on the wafer.

[0003] Through such repeated lamination steps, electrically active patterns are produced in the integrated circuit. If the individual structures are not aligned within the tolerances allowed by the production process, interference occurs between the electrically active patterns, which can cause problems in the performance and reliability of the manufactured circuits. To measure and verify the alignment errors between these layers, the focus position is found based on the brightness or phase difference in the image of the wafer.

[0004] However, conventionally, the laser reflecting surface is not constant due to the autofocus function, and there has been a problem in that the focal position cannot be accurately found. Summary of the Invention [Problem to be solved by the invention]

[0005] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, the present invention provides an overlay measurement apparatus that controls focus movement to find an accurate focus distance, and a program storage medium therefor.

[0006] The object of the present invention is not limited to the object mentioned above, and other objects and advantages of the present invention not mentioned can be understood from the following description and can be more clearly understood from the embodiments of the present invention. In addition, it is easy to understand that the object and advantages of the present invention can be realized by the means and combinations thereof described in the claims. [Means for solving the problem]

[0007] To achieve this objective, an overlay measurement apparatus for controlling focus movement according to one embodiment of the present invention includes an illumination unit configured to direct illumination to an overlay measurement target; a collection unit including an objective lens and a detector to acquire one or more focused images of the target; a lens focus actuator that operates the objective lens to adjust its distance from the wafer; and a processor that controls the operation of the lens focus actuator, wherein the processor can acquire focus graphs for each of two layers from the one or more focused images, identify a reference focus for the acquired focus graphs, and move the objective lens.

[0008] In addition, a method for controlling focus movement of an overlay measurement apparatus according to an embodiment of the present invention may include the steps of acquiring a focus graph for each of two layers from one or more focused images, and identifying a reference focus for the acquired focus graph and moving an objective lens.

[0009] In addition, in a computer-readable storage medium including a program including commands for controlling focus movement of an overlay measurement apparatus according to an embodiment of the present invention, the program may include commands for acquiring focus graphs for each of two layers from one or more focused images, and commands for identifying a reference focus for the acquired focus graph and moving an objective lens. Effect of the Invention

[0010] The present invention can search for a high-brightness focus position by controlling the movement of the objective lens via a lens focus actuator so as to move the position of the reference focus in the measurement image using the difference between the reference focus and the focus in the measurement image.

[0011] Moreover, the present invention can identify the light and dark indexes of the two layers of the measurement image by identifying the reference focus through the two focus graphs of the reference image.

[0012] The present invention can also determine the focal length of the objective lens by subtracting the difference between the reference focus and the identified focus from the value of the reference focus.

[0013] The above-mentioned effects and specific effects of the present invention will be described in conjunction with the following description of the preferred embodiment of the invention. [Brief description of the drawings]

[0014] [Figure 1] 1 is a conceptual diagram of an overlay measurement apparatus according to an embodiment of the present invention; [Diagram 2] 4 is a flow chart illustrating a method for controlling focus movement of an overlay measurement apparatus according to an embodiment of the present invention. [Diagram 3] FIG. 13 is an exemplary diagram illustrating a focus graph for two layers according to an embodiment of the present invention. [Figure 4] Fig. 4(a) is an example diagram showing focus graphs for two layers of a reference image according to an embodiment of the present invention. Fig. 4(b) is an example diagram showing brightness indexes for a reference focus in two layers of an image acquired according to an embodiment of the present invention. Fig. 4(c) is an example diagram in which the brightness index difference acquired in Fig. 4(b) is applied to a focus graph for the image in Fig. 4(a). Fig. 4(d) is an example diagram in which the reference focus is adjusted based on the focus difference acquired in Fig. 4(c). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The above-mentioned objects, features and advantages will be described in detail below with reference to the accompanying drawings, so that a person having ordinary skill in the art to which the present invention pertains can easily implement the technical idea of ​​the present invention. In describing the present invention, if a detailed description of a known technology according to the present invention is deemed to make the gist of the present invention unclear, the detailed description will be omitted. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings are used to indicate the same or similar components.

[0016] Although the terms "first", "second", etc. are used to describe various components, it is understood that these components are not limited by these terms. These terms are used merely to distinguish one component from another, and it is understood that a first component may also be a second component unless otherwise specified.

[0017] Hereinafter, when an arbitrary structure is arranged on the "top (or bottom)" of a component or "above (or below)" a component, it means that the arbitrary structure is not only arranged in contact with the upper surface (or lower surface) of the component, but also that other structures may be interposed between the component and the arbitrary structure arranged on (or below) the component.

[0018] In addition, when a component is described as being "coupled," "coupled," or "connected" to another component, it should be understood that the components may be directly coupled or connected to each other, but that other components may be "intervening" between each component, or each component may be "coupled," "coupled," or "connected" via other components.

[0019] Throughout the specification, unless otherwise specified to the contrary, each element may be singular or plural.

[0020] As used herein, singular expressions include plural expressions unless the context clearly indicates otherwise. Terms such as "comprise" or "include" in this application should not be interpreted as including all of the multiple components or multiple steps described in the specification, and should be interpreted as including some of the components or some steps that may not be included or may further include additional components or steps.

[0021] Throughout the specification, "A and / or B" means A, B, or A and B, unless otherwise specified, and "C to D" means C or more and D or less, unless otherwise specified.

[0022] Hereinafter, an overlay measurement apparatus and method for controlling focus movement and a program storage medium therefor according to some embodiments of the present invention will be described.

[0023] FIG. 1 is a conceptual diagram of an overlay measurement apparatus according to an embodiment of the present invention.

[0024] Referring to FIG. 1, an overlay metrology apparatus 100 according to one embodiment of the present invention is an apparatus for measuring an error between a first overlay mark (OM1) and a second overlay mark (OM2) formed on different layers formed on a wafer 140.

[0025] For example, 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 in the scribe lane while forming layers to form a semiconductor device in the die area. For example, the first overlay mark (OM1) may be formed with an insulating film pattern, and the second overlay mark (OM2) may be formed with a photoresist pattern formed on the insulating film pattern.

[0026] In this case, the second overlay mark (OM2) is exposed to the outside, while the first overlay mark (OM1) is obscured 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. Also, although the physical positions of the first overlay mark (OM1) and the second overlay mark (OM2) are different, their focal planes may be the same or different.

[0027] The overlay metrology apparatus 100 according to an embodiment of the present invention may include a light source 110, a first beam splitter 112, a first mirror 113, a first color filter 114, a second color filter 115, a beam combiner 116, a second mirror 117, a relay lens 118, a polarizing filter 121, an aperture 151, a second detector 133, a focus actuator 134, a zoom lens 132, a first detector 131, a second beam splitter 130, an optical element 127, a third beam splitter 124, a lambda wave plate 122, an objective lens 120, a lens focus actuator 125, an aperture 151, an AF 161, and a processor 170. The present invention may replace the first and second color filters with various filters. And, the color filter may include at least one of a filter wheel, a linear translation device, and a flipper device.

[0028] For example, the first detector 131, the second beam splitter 130, the zoom lens 132, the second detector 133, and the actuator 134 are configured to direct illumination to an overlay metrology target, which may be referred to as an illumination section. The illumination section may direct illumination from at least one illumination source to an overlay metrology target. For example, the overlay metrology target may include a wafer.

[0029] For example, the light source 110, the first beam splitter 112, the first mirror 113, the first color filter 114, the second color filter 115, the beam combiner 116, the second mirror 117, the aperture 151, the relay lens 118, the polarizing filter 121, the lambda wave plate 122, and the third beam splitter 124 are configured to obtain one or more focused images of a target and can be referred to as a collection unit. For example, the collection unit can include an objective lens and a detector.

[0030] The configuration of the overlay measurement apparatus 100 shown in Fig. 1 is according to one embodiment, and the components of the overlay measurement apparatus 100 are not limited to the embodiment shown in Fig. 1, and some components may be added, changed, or deleted as necessary. For example, the overlay measurement apparatus 100 may include a memory (not shown) that stores commands, programs, logic, etc. for controlling the operation of each component of the overlay measurement apparatus 100 by the processor 170.

[0031] According to one embodiment, the light source 110 may be a halogen lamp, a xenon lamp, a supercontinuum laser, a light emitting diode, a laser induced lamp, or the like.

[0032] According to one embodiment, the first beam splitter 112 is responsible for splitting the beam emitted from the light source 110 into two beams. The first beam splitter 112 transmits a portion of the beam emitted from the light source 110 and reflects a portion of the beam, thereby splitting the beam emitted from the light source 110 into two beams.

[0033] According to one embodiment, the first mirror 113 is disposed between the first beam splitter 112 and the second spectral filter 115 to redirect the beam reflected by the first beam splitter 112 towards the second spectral filter 115.

[0034] According to one embodiment, the first spectral filter 114 serves to adjust the central wavelength and bandwidth of the beam split by the first beam splitter 112 to be suitable for image acquisition of the second overlay mark (OM2) formed on the current layer. The spectral filter can be one of a filter wheel, a linear translation device, and a flipper device.

[0035] According to one embodiment, the second spectral filter 115 serves to adjust the center wavelength and bandwidth of the beam reflected by the first beam splitter 112 among the beams separated from the first beam splitter 112 to be suitable for image acquisition of the first overlay mark (OM1) formed in the previous layer.

[0036] According to an embodiment, the beam combiner 116 serves to combine the light that has passed through the first spectrum filter 114 and the second spectrum filter 115. The light that has passed through the first spectrum filter 114 passes through the beam combiner 116, and the beam that has passed through the second spectrum filter 115 has its path changed by the second mirror 117 to be directed toward the beam combiner 116, and is then reflected by the combiner 116 and further combined with the beam that has passed through the beam combiner 116, and passes through the aperture 151.

[0037] According to one embodiment, the aperture 151 (eg, a pinhole) serves to modify the beam transmitted by the beam combiner into a form suitable for imaging the first overlay mark (OM1).

[0038] According to one embodiment, the second detector 133 detects the beam reflected by the second beam splitter 130. The second detector 133 is mounted on a focus actuator 134 to adjust the distance between the second beam splitter 130 and the second detector 133. The second detector 133 captures an image of the first overlay mark (OM1).

[0039] According to one embodiment, the first detector 131 detects the beam that has passed through the second beam splitter 130. The first detector 131 can capture an image of the second overlay mark (OM2).

[0040] Alternatively, depending on the user's settings, the second detector can be inoperative and image acquisition of the first overlay mark (OM1) and the second overlay mark (OM2) can be performed only by the first detector.

[0041] According to an embodiment, the zoom lens 132 is disposed between the second beam splitter 130 and the focus actuator 134. The zoom lens 132 receives a position change value of the second detector 133 from the focus actuator 134, and serves to match the magnification of the image of the second overlay mark (OM2) and the image of the first overlay mark (OM1) based on the position change value. Due to the height difference between the first overlay mark (OM1) and the second overlay mark (OM2), the optical path distance between the second detector 133 and the second beam splitter 130 is different from the optical path distance between the first detector 131 and the second beam splitter 130, so that the magnification of the image acquired by the first detector 131 and the image acquired by the second detector 133 may be different. In order to measure the overlay error accurately, the magnification must be matched.

[0042] According to an embodiment, the second beam splitter 130 is responsible for splitting the beam collected by the objective lens 120 into two beams. The second beam splitter 130 may include a tube beam splitter and a dichroic filter. A dichroic filter is a filter that transmits a beam of a specific wavelength. The beam collected by the objective lens 120 passes through the lambda wave plate 122, the third beam splitter 124, and the optical element 127, and is then split into two beams by the second beam splitter 130. That is, the beam is split into a beam suitable for detecting the first overlay mark (OM1) and a beam suitable for detecting the second overlay mark (OM2).

[0043] According to one embodiment, the optical element 127 may include a hot mirror and a cold mirror.

[0044] According to one embodiment, the third beam splitter 124 serves to further split the beam combined via the combiner 116 into two beams. The beam combined via the beam combiner 116 is polarized via the relay lens 118 and the polarizing filter 121 and then split into two beams at the third beam splitter 124.

[0045] According to one embodiment, the objective lens 120 serves to focus the circularly polarized beam, which is combined by the combiner 116, reflected by the third beam splitter 124, and passed through the lambda wave plate 122, onto a measurement position on the wafer 140, and collect the reflected beam at the measurement position. The objective lens 120 is mounted on a lens focus actuator 125.

[0046] According to one embodiment, the lens focus actuator 125 can adjust the distance between the objective lens 120 and the wafer 140 so that the focal plane is located at the first overlay mark (OM1) or the second overlay mark (OM2). Under the control of the processor 170, the lens focus actuator 125 can move the objective lens 120 vertically towards the wafer (e.g., in the Y direction) to adjust the focal length.

[0047] According to one embodiment, the optical element 127 is placed at 45° to the path of the beam transmitted through the beam splitter to direct the beam to the autofocus module, characterized by reflecting the long wavelength beam and transmitting the short wavelength beam, or reflecting the short wavelength beam and transmitting the long wavelength beam. The optical element can be one of a hot mirror or a cold mirror.

[0048] The autofocus sensor obtains a signal according to the focus position from the light reflected from the measurement area of ​​the wafer, and can adjust an actuator that adjusts the distance between the measurement area of ​​the wafer and the objective lens to adjust the focus position.

[0049] During focus scanning, a first image, e.g., a reference image, may be acquired for each measurement point in the first detector 131. For example, the reference image may include one or more focused images.

[0050] According to one embodiment, the processor 170 may obtain focus graphs (e.g., first and second focus graphs) for each of two layers (e.g., first and second layers) of a first image (e.g., reference image), and identify a reference focus for the obtained focus graph as one of the focus, the layer-specific maximum value, and the minimum maximum value between both lasers. For example, the processor 170 may determine a focus (e.g., 395) that falls between a first maximum brightness index (e.g., 350) in the first focus graph and a second maximum brightness index (e.g., 440) in the second focus graph as the reference focus.

[0051] According to an embodiment, when a measurement image is acquired from a detector, the processor 170 may identify a light / dark index based on each of focus graphs (e.g., third and fourth focus graphs) of two layers (e.g., third and fourth layers) of the acquired measurement image based on the identified reference focus. The processor 170 may acquire an image corresponding to a current position of the objective lens 120 via the detector. The processor 170 may then acquire an image based on the movement of a stage on which the wafer 140 is placed.

[0052] According to one embodiment, processor 170 may identify a reference focus (e.g., 500) using a first focus graph of a first layer and a second focus graph of a second layer of a first image (e.g., a reference image). Processor 170 may then identify two third lightness and darkness indices for the identified reference focus based on a third focus graph of a second image (e.g., a measurement image), and identify two fourth lightness and darkness indices for the identified reference focus based on a fourth focus graph of the measurement image.

[0053] According to an embodiment, the processor 170 may identify one third light and dark index and one fourth light and dark index having the shortest focus distance between two third light and dark indexes and two fourth light and dark indexes, and may determine whether a focus value corresponding to the identified one third light and dark index is the same as a focus value corresponding to the identified one fourth light and dark index.

[0054] According to one embodiment, the processor 170 can identify a focus corresponding to each of the identified light and dark indices through each of the two layers of the reference image and calculate the difference (e.g., 50) between the reference focus (e.g., 500) and the identified focus 550.

[0055] Then, the processor 170 can move the objective lens 120 to a focus corresponding to the measurement image based on the calculated difference. The processor 170 can control the lens focus actuator 125 to adjust the focal length of the objective lens 120.

[0056] For example, processor 170 may subtract the calculated difference from the reference focus value and operate the lens focus actuator 125 to move the objective lens 120 to a position corresponding to the subtracted focus position.

[0057] According to one embodiment, the processor 170 can control the movement of the objective lens 140 via the lens focus actuator 125 based on the calculated difference for each measurement point on the wafer.

[0058] These processors 170 may be configured separately within the overlay metrology tool, or may be programmed and stored in other components.

[0059] FIG. 2 is a flow chart showing a method of controlling focus movement of an overlay measurement apparatus according to an embodiment of the present invention. FIG. 3 is an example diagram showing focus graphs of two layers according to an embodiment of the present invention. FIG. 4(a) is an example diagram showing focus graphs for two layers of a reference image according to an embodiment of the present invention. FIG. 4(b) is an example diagram showing brightness indexes for a reference focus in two layers of an acquired image according to an embodiment of the present invention. FIG. 4(c) is an example diagram in which the brightness index difference acquired in FIG. 4(b) is applied to a focus graph for the image in FIG. 4(a). FIG. 4(d) is an example diagram in which the reference focus is adjusted based on the focus difference acquired in FIG. 4(c).

[0060] Hereinafter, a method for controlling focus movement of an overlay measurement apparatus according to an embodiment of the present invention will be described in detail with reference to FIGS. 2, 3, and 4(a) to 4(d).

[0061] According to one embodiment, the processor 170 can identify whether the overlay metrology tool is to begin measurement (S210). The processor 170 can determine whether to begin an operation to measure the brightness of a measurement point (e.g., site) at the first detector.

[0062] According to one embodiment, the processor 170 can obtain a focus graph for each of the two layers of the reference image (S212). When it is determined that an operation for measuring brightness on the wafer is to start, the processor 170 can obtain a focus graph for each of the two layers of the reference image from a memory (not shown).

[0063] Referring to FIG. 3, an image may include multiple layers (e.g., two layers), each of which may have different brightness levels at different focus positions, and the processor 170 may identify a focus graph that indicates the brightness levels of the layers via brightness indexes at each of these focus positions.

[0064] For example, the first focus graph 310 indicates a lightness / darkness index for a first layer (eg, a previous layer), and the second focus graph 320 indicates a lightness / darkness index for a second layer (eg, a current layer).

[0065] For example, the first focus graph 310 has a maximum light / dark index of 35 at a focus of 440, and the second focus graph 320 has a maximum light / dark index of 35 at a focus of 350.

[0066] For example, there are two focuses (440, 520) with the same light / dark index (eg, 19) in one focus graph (eg, first focus graph 310).

[0067] In this manner, the processor 170 can obtain focus graphs for each of the two layers of the reference image when it is determined that an operation to measure brightness for the wafer is to commence.

[0068] According to an embodiment, the processor 170 may identify a reference focus for the acquired focus graph (S214). The processor 170 may determine the reference focus as one of the focus point, the layer-specific maximum value, and the minimum maximum value between the two layers using the focus graphs of each of the two layers in the reference image. The processor 170 may identify a focus position having a maximum light-dark index through each focus graph.

[0069] 4(a), the processor 170 can obtain a reference image. The processor 170 can then identify a focus (e.g., 460) having a maximum brightness index (e.g., 5) through a first focus graph 411 of a first layer (e.g., previous layer) in the reference image. The processor 170 can also identify a focus (e.g., 540) having a maximum brightness index 3 through a second focus graph 412 of a second layer (e.g., current layer).

[0070] Then, the processor 170 can identify the focus position (e.g., 500) of the reference focus 413 using the focus positions (e.g., 460, 540) corresponding to the maximum brightness and darkness indexes (e.g., 5, 3) in each layer (e.g., first layer, second layer).

[0071] For example, processor 170 may determine the middle of the focus positions (eg, 460, 540) having the maximum light-dark index (eg, 5, 3) as the focus position (eg, 500) for reference focus 413.

[0072] According to one embodiment, the processor 170 may identify whether a measurement image is to be acquired (S216). The processor 170 may acquire a measurement image from the detector for the wafer to be measured.

[0073] According to one embodiment, the processor 170 can identify a light / dark index based on the two layers of the measurement image (e.g., a virtual focus graph of the two layers) based on the reference focus (S218). Once the measurement image for the wafer is acquired, the processor 170 can identify a light / dark index for each of the two layers of the acquired measurement image based on the reference focus.

[0074] The processor 170 can use the reference focus 413 in the reference image to identify a light / dark index for each of the two layers of the measurement image.

[0075] Referring to (b) of Figure 4, the processor 170 can identify a first brightness index (e.g., 1.75) based on a first focus graph 421 for the first layer of the measurement image and a second brightness index (e.g., 3) based on a second focus graph 422 for the second layer based on a reference focus 413 of the reference image.

[0076] For example, although the first focus graph 421 and the second focus graph 422 are shown in Fig. 4 for purposes of illustrating the invention, the processor 170 may not generate the first focus graph 421 for the first layer and the second focus graph 422 for the second layer, i.e., the processor 170 may identify the lightness and darkness indexes of the two layers of the measurement image based on the reference focus when the measurement image is acquired.

[0077] According to one embodiment, the processor 170 can identify a focus corresponding to each of the brightness indexes identified in each of the two layers of the reference image (S220). The processor 170 can calculate the difference between the first brightness index (e.g., 1.75) and the second brightness index (e.g., 3) identified in the above step (S218), and identify an index having the same difference as the calculated difference through two focus graphs of the reference image.

[0078] The processor 170 may calculate a brightness index difference (e.g., 3-1.75=1.25) based on two focus graphs 421 and 422 of the measurement image using the reference focus 413 as a reference. The processor 170 may then determine a focus position corresponding to the calculated brightness index difference (e.g., 1.25) through the two focus graphs in the reference image.

[0079] Referring to FIG. 4(c), the processor 170 can determine where the focus is that has the same brightness index difference as the brightness index difference (eg, 1.25) of FIG. 4(b).

[0080] For example, processor 170 may determine that there are two points in the first focus graph 411 with a light-dark index of 1.75, and two points in the second focus graph 412 with a light-dark index of 3. Processor 170 may then identify points (e.g., 433, 434) where the focus is the same between the two points in the first focus graph 411 and the two points in the second focus graph 412.

[0081] In this manner, the processor 170 can determine that the points that are identical to the light / dark index difference (e.g., 1.25) in (b) of FIG. 4 are the first point 434 in the first focus graph 411 and the second point 433 in the second focus graph 412, and can determine this as the identified focus.

[0082] According to one embodiment, processor 170 may calculate a difference between the reference focus and the identified focus (S222). Processor 170 may calculate a focus difference (e.g., 50) by subtracting the reference focus value, 500, from the identified focus value (e.g., 550).

[0083] According to one embodiment, processor 170 can move the objective lens to a focus corresponding to the measurement image based on the calculated difference (S224). Processor 170 can use the focus difference to determine a reference focus in the measurement image.

[0084] Referring to FIG. 4(d), the processor 170 can control the lens focus actuator 125 to adjust the focal length of the objective lens 120 to a position 450 of the focus 433 identified by the position (e.g., 500) of the reference focus 413.

[0085] As described above, the present invention can identify a reference focus via focus graphs for each of the two layers of the reference image, and find the focus position with the highest brightness in the measurement image by adjusting the focal length of the objective lens 120 based on the difference between the identified reference focus and the focus identified via the measurement image.

[0086] The steps in each of the above-described procedure diagrams may be performed out of the order shown or simultaneously. Furthermore, at least one component of the present invention and at least one operation performed by the at least one component may be embodied in hardware and / or software.

[0087] As described above, the present invention has been described with reference to the illustrative drawings, but the present invention is not limited to the embodiments and drawings disclosed in this specification, and it is clear that various modifications can be made by those skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration of the present invention are not explicitly described and explained while the embodiments of the present invention are described above, it is natural that the effects that can be predicted by the configuration should also be recognized. [Explanation of symbols]

[0088] 100 Overlay measurement device 110 Light source 112 First beam splitter 113 Mirror No. 1 114 1st Spectrum Filter 115 Second Spectrum Filter 116 Beam Combiner 117 2nd Mirror 118 Relay Lens 120 Objective Lens 121 Polarizing Filter 122 Lambda Wave Plate 124 3rd Beam Splitter 125 Lens Focus Actuator 127 Optical Elements 130 Second beam splitter 131 First detector 132 Zoom Lens 133 Second detector 134 Focus Actuator 151 Aperture 161AF 170 Processors

Claims

1. In an overlay measurement apparatus that controls focus movement, an illumination unit configured to direct illumination at the overlay metrology target; a collection section including an objective lens and a detector for acquiring one or more focused images of the target; A lens focus actuator that moves the objective lens to adjust the distance between the objective lens and the wafer; and a processor for controlling operation of the lens focus actuator; The processor, obtaining a focus graph for each of the two layers from the one or more focused images; configured to identify a reference focus for the acquired focus graph and move the objective lens; When a measurement image is acquired, identifying lightness / darkness indices for two layers of the acquired measurement image based on the identified reference focus; identifying a focus corresponding to each of the identified brightness and darkness indices in each of the two layers of the one or more focused images; identifying the reference focus based on a first focus graph of a first layer and a second focus graph of a second layer of the one or more focused images; identifying two third light and dark indices of the measurement image; Identifying two fourth light and dark indices of the measurement image; Identifying one third bright / dark index and one fourth bright / dark index having a shortest focus distance between the two third bright / dark indexes and the two fourth bright / dark indexes; Calculating a difference between the reference focus and the identified focus; configured to move the objective lens to a focus corresponding to the measurement image based on the calculated difference. Overlay measurement equipment.

2. The processor, In each of the two layers, a reference focus for the obtained focus graph is set to be identified as one of a focus, a layer-specific maximum, or a minimum maximum between the two layers. The overlay metrology apparatus according to claim 1 .

3. The processor, and determining whether a focus value corresponding to the identified one third light / dark index and a focus value corresponding to the identified one fourth light / dark index are the same. The overlay metrology apparatus according to claim 1 .

4. The processor, subtracting the calculated difference from the reference focus value; activating the lens focus actuator to move the objective lens to a position corresponding to the subtracted focus position; The overlay metrology apparatus according to claim 1 .

5. The processor, configured to control movement of the objective lens via the lens focus actuator based on the calculated difference for each measurement point on the wafer. The overlay metrology apparatus according to claim 1 .

6. The processor, configured to obtain an image corresponding to a current position of the objective lens via the detector; The overlay metrology apparatus according to claim 1 .

7. The processor, configured to acquire images based on movement of a stage on which the wafer is positioned; The overlay measurement apparatus according to claim 6 .

8. 1. A method for controlling focus movement of an overlay metrology apparatus, comprising: obtaining a focus graph for each of the two layers from one or more focused images; and identifying a reference focus for the acquired focus graph and moving an objective lens; The step of moving the objective lens includes: when a measurement image is acquired, identifying lightness / darkness indices for two layers of the acquired measurement image based on the identified reference focus; and identifying a focus corresponding to each of the identified brightness and darkness indices in each of the two layers of the one or more focused images; The step of identifying a focus corresponding to each of the identified light and dark indices comprises: identifying the reference focus using a first focus graph in a first layer and a second focus graph in a second layer of the one or more focused images; identifying two third lightness and darkness indices of the measurement image; and identifying two fourth light and dark indices of the measurement image; Further comprising the step of identifying one third light index and one fourth light index having a shortest focus distance between the two third light indexes and the two fourth light indexes; calculating a difference between the reference focus and the identified focus; and moving the objective lens to a focus corresponding to the measurement image based on the calculated difference. A method for controlling focus movement of an overlay metrology tool.

9. The step of identifying a reference focus includes: identifying, in each of the two layers, a reference focus for the obtained focus graph as one of a focus, a layer-wise maximum, or a minimum maximum between the two layers; The method for controlling focus movement of an overlay metrology apparatus according to claim 8.

10. The step of identifying the one third light and dark index and the one fourth light and dark index includes: determining whether a focus value corresponding to the identified one third lightness index and a focus value corresponding to the identified one fourth lightness index are the same; The method for controlling focus movement of an overlay metrology apparatus according to claim 8.

11. The step of moving the objective lens includes: subtracting the calculated difference from the reference focus value; and moving the objective lens to correspond to the subtracted focus position; The method for controlling focus movement of an overlay metrology apparatus according to claim 8.

12. controlling movement of the objective lens based on the calculated difference for each measurement point on the wafer. The method for controlling focus movement of an overlay metrology apparatus according to claim 8.

13. and acquiring an image corresponding to a current position of the objective lens. The method for controlling focus movement of an overlay metrology apparatus according to claim 8.

14. A computer-readable storage medium including a program including instructions for controlling focus movement of an overlay metrology device, The program is A command to obtain a focus graph for each of the two layers from one or more focused images; and a command for identifying a reference focus for the acquired focus graph and moving an objective lens; a command for identifying, when a measurement image is acquired, lightness / darkness indices for two layers of the acquired measurement image based on the identified reference focus; and instructions for identifying a focus corresponding to each of the identified light and dark indices in each of the two layers of the one or more focus-specific images; A command for identifying a focus corresponding to each of the identified light and dark indexes is a command for identifying the reference focus using a first focus graph in a first layer and a second focus graph in a second layer of the one or more focus-specific images; a command identifying two third light and dark indexes of the measurement image; and a command for identifying two fourth light and dark indexes of the measurement image; The method further includes a command for identifying one third light index and one fourth light index having a shortest focus distance between the two third light indexes and the two fourth light indexes, instructions for calculating a difference between the reference focus and the identified focus; and a command to move the objective lens to a focus corresponding to the measurement image based on the calculated difference; A computer readable storage medium for controlling focus movement of an overlay metrology device.

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