Recipe generation method and overlay measurement device having recipe generation function

Abstract

The present invention relates to a recipe generation method for an overlay measurement device and, more specifically, to a recipe generation method including a reference alignment mark image. The present invention provides the recipe generation method for automatically generating a recipe of an overlay measurement device, comprising the steps of: acquiring an optimal parameter candidate set; setting the overlay measurement device to an existing parameter set; using an existing reference alignment mark image so as to position an alignment mark within a measurement range of the overlay measurement device set to the existing parameter set; setting the overlay measurement device to the optimal parameter candidate set; acquiring a new reference alignment mark image corresponding to the optimal parameter candidate set by photographing the alignment mark with the overlay measurement device set to the optimal parameter candidate set; and generating an optimal candidate recipe including the optimal parameter candidate set and the new reference alignment mark image.

Description

Overlay measuring device equipped with a recipe generation method and recipe generation function

[0001] The present invention relates to a method for generating a recipe for an overlay measuring device, and more specifically, to a method for generating a recipe including a reference alignment mark image.

[0002] Multiple pattern layers are sequentially formed on a semiconductor substrate. Additionally, a circuit of a single layer may be divided into two patterns through double patterning. Only when these pattern layers or multiple patterns of a single layer are accurately formed at predetermined locations can a desired semiconductor device be manufactured.

[0003] Therefore, to verify whether the pattern layers are accurately aligned, overlay marks, which are alignment marks formed simultaneously with the pattern layers, are used.

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

[0005] Then, through an overlay measuring device, an image of the overlay structure of the pattern layer formed in the previous process (an image obtained by passing through the photoresist layer) and an image of the overlay structure of the photoresist layer are obtained. The overlay measuring device measures the offset value between the centers of these images to measure the overlay error (alignment error) value.

[0006] FIG. 1 is a plan view of an example of an overlay mark. The overlay mark (1) illustrated in FIG. 1 has four sets of working zones (4, 5, 6, 7). Each set of working zones (4, 5, 6, 7) has two working zones arranged diagonally opposite each other. Each set of working zones (4, 5, 6, 7) is used to measure the overlay error in the X-axis or Y-axis direction of the pattern layer formed together with the corresponding set of working zones. To prevent interference, the structures (2) formed together with the first pattern layer and the structures (3) formed together with the second pattern layer are arranged so that they do not overlap each other.

[0007] Each working zone includes bars arranged at regular intervals from the center of the overlay mark (1) to the outer edge of the overlay mark (1). Thus, using an overlay measuring device, periodic signals as shown in FIG. 2 can be obtained from each of the two working zones belonging to the set of working zones (4, 5, 6, 7). The graph of FIG. 2 can be obtained, for example, by projecting a selected portion of area (8) in FIG. 1 in the Y-axis direction. That is, a graph as shown in FIG. 2 can be obtained by adding the gray values ​​of pixels with the same X value.

[0008] In the graph of FIG. 2, peaks appear in the areas where the bars are placed. Since the conventional overlay mark (1) has bars placed periodically, the acquired signal also has periodicity. Then, the overlay error is measured through correlation analysis of two periodic signals acquired from two selected areas (8, 8').

[0009] The overlay measuring device used for such overlay error measurement requires high precision and reliability, and to achieve this, complex measurement conditions and various variables must be appropriately set.

[0010] For example, it is necessary to optimize parameters such as the wavelength band of the illumination of the overlay measurement device, the numeric aperture value (NA), the focus position, and the size of the pinhole.

[0011] Conventionally, a method of sequentially optimizing these parameters has been used. For example, by fixing other parameters, acquiring and measuring overlay mark images for each illumination wavelength band, and evaluating the quality of the overlay mark images and / or the performance of the overlay measurement device using various quality metrics, the optimal illumination wavelength band can be selected.

[0012] Quality indicators for evaluating image quality may include, for example, Modulation Transfer Function (MTF), Mean Squared Error (MSE), and Root Mean Square (RMS). Additionally, quality indicators for evaluating the performance of an overlay measurement device may include, for example, Final Residual 3 Sigma, Tool Induced Shift (TIS) 3 Sigma, Registration 3 Sigma, Total Measurement Uncertainty (TMU), and Move and Measure (MAM) time.

[0013] Once the optimal lighting wavelength band is selected, the lighting wavelength band is fixed at that optimal band, and the optimal numeric aperture value can be selected through quality evaluation based on the numeric aperture value. In the same way, the optimal focus position, optimal pinhole size, etc., can also be selected sequentially.

[0014] However, since this method does not consider the interactions between parameters, it is difficult to regard the parameters selected by this method as the optimal set of parameters.

[0015] Therefore, instead of optimizing parameters sequentially, a method of optimizing by evaluating parameters in sets was proposed.

[0016] To optimize parameters in this way, a set of candidate parameters must be selected, each set of candidate parameters applied to an overlay measurement device to acquire an overlay mark image, and the quality of the acquired overlay mark image and / or the performance of the overlay measurement device must be evaluated.

[0017] In order to acquire an overlay mark image, the overlay measuring device needs to recognize the location of the overlay mark. To do this, a reference alignment mark image corresponding to the corresponding set of candidate parameters is required. The overlay measuring device finds a part in the captured image that matches the reference alignment mark image. Through this, the location of the overlay mark to be measured can be detected.

[0018] Each candidate parameter set requires a corresponding reference alignment mark image, and using different reference alignment mark images may result in errors during the overlay mark image acquisition process.

[0019] [Prior Art Literature]

[0020] 1. Korean Published Patent Application 10-2024-0089163

[0021] 2. Korean Published Patent Application 10-2024-0067834

[0022] 3. Korean Registered Patent Publication 10-2546552

[0023] 4. Korean Registered Patent Publication 10-2519813

[0024] The present invention aims to provide a method for generating a recipe including various parameter values ​​and a reference alignment mark image, and an overlay measuring device equipped with a function for generating such a recipe.

[0025] To achieve the above-mentioned objective, the present invention provides a method for automatically generating a recipe for an overlay measuring device, comprising the steps of: acquiring a set of optimal parameter candidates; setting the overlay measuring device with an existing set of parameters; positioning an alignment mark within the measurement range of the overlay measuring device set with the existing set of parameters using an existing reference alignment mark image; setting the overlay measuring device with the set of optimal parameter candidates; capturing the alignment mark with the overlay measuring device set with the set of optimal parameter candidates to acquire a new reference alignment mark image corresponding to the set of optimal parameter candidates; and generating an optimal candidate recipe including the set of optimal parameter candidates and the new reference alignment mark image.

[0026] Additionally, the above step a) comprises a-1) a step of selecting at least one measurement target site; a-2) a step of obtaining overlay mark images for each parameter set by photographing an overlay mark located at the measurement target site while changing the parameter values ​​of the overlay measurement device; a-3) a step of calculating quality indicator values ​​for each parameter set by analyzing the overlay mark images; and a-4) a step of selecting at least one optimal parameter candidate set based on the quality indicator values ​​for each parameter set. The present invention provides a recipe generation method comprising these steps.

[0027] Additionally, the above quality indicator value provides a recipe generation method comprising at least one of the clarity of the layered structure included in the overlay mark image, the periodicity, repeatability, and symmetry of the grid.

[0028] In addition, the above step a-4) provides a recipe generation method, which is a step of selecting the set of optimal parameter candidates through Response Surface Methodology.

[0029] In addition, the above alignment mark provides a recipe generation method in which the alignment mark is a global alignment mark for aligning the wafer or an overlay mark for aligning between pattern layers formed on the wafer.

[0030] In addition, the present invention provides an overlay measurement device comprising an imaging system configured to acquire an alignment mark image and a controller communicably coupled to the imaging system, wherein the controller comprises at least one memory including instructions and a processor configured to execute the instructions included in the at least one memory, and the processor executes the instructions to perform the steps of: a) acquiring an optimal parameter candidate set; b) setting the overlay measurement device with an existing parameter set; c) positioning an alignment mark within the measurement range of the overlay measurement device set with the existing parameter set using an existing reference alignment mark image; d) setting the overlay measurement device with the optimal parameter candidate set; e) capturing the alignment mark with the overlay measurement device set with the optimal parameter candidate set to acquire a new reference alignment mark image corresponding to the optimal parameter candidate set; and f) generating an optimal candidate recipe including the optimal parameter candidate set and the new reference alignment mark image.

[0031] According to the present invention, since a recipe including various parameter values ​​and reference alignment mark images can be automatically generated, errors caused by manual work can be minimized and efficiency can be increased.

[0032] In addition, unlike conventional sequential parameter optimization methods, the accuracy and reliability of overlay measurements can be improved by deriving a set of optimal parameter candidates that considers the interactions between parameters.

[0033] Figure 1 is a plan view of an example of an overlay mark.

[0034] Figure 2 shows a signal obtained from one working zone of the overlay mark shown in Figure 1.

[0035] FIG. 3 is a schematic diagram of an overlay measuring device according to an embodiment of the present invention.

[0036] FIG. 4 is a flowchart of a recipe generation method according to an embodiment of the present invention.

[0037] Figure 5 is a flowchart of an example of the steps for obtaining a set of optimal parameter candidates.

[0038] Figure 6 is a diagram showing measurement sites on a semiconductor wafer marked with dots.

[0039] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. However, embodiments of the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted 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. Accordingly, the shapes of elements in the drawings are exaggerated to emphasize clearer explanations, and elements indicated by the same reference numeral in the drawings represent the same elements.

[0040] FIG. 3 is a schematic diagram of an overlay measuring device according to an embodiment of the present invention.

[0041] As illustrated in FIG. 3, the overlay measuring device (10) includes an imaging system (100) configured to acquire an alignment mark image including an overlay mark image and a global alignment mark image, and a controller (200). The overlay measuring device (10) acquires an image by photographing a semiconductor wafer (W) on which a global alignment mark and an overlay mark are formed. Then, the acquired alignment mark image is analyzed to measure the overlay error between pattern layers formed on the wafer (W).

[0042] The imaging system (100) of the overlay measuring device (10) includes an illumination optical system (110) that illuminates an alignment mark on a semiconductor wafer (W), an imaging optical system (120) that collects reflected light from the alignment mark to form an alignment mark image, an image detector (130) that acquires the alignment mark image formed by the imaging optical system (120), and a stage (140) on which the semiconductor wafer (W) is placed.

[0043] The illumination optical system (110) can be constructed using various optical elements. For example, the illumination optical system (110) may include a light source (111), a pinhole (115), a beam splitter (116), and an objective lens (118). Additionally, it may include a lens (113) positioned between the pinhole (115) and the light source (111).

[0044] The light source (111) may include a light source capable of generating light of a wide wavelength band and variable optical filters capable of adjusting the wavelength band of the transmitted light.

[0045] The beam splitter (116) is positioned between the light source (111) and the objective lens (118) and serves to transmit light from the light source (111) to the objective lens (118).

[0046] The objective lens (118) serves to concentrate light onto a measurement position on the surface of the semiconductor wafer (W) and to collect reflected light from the measurement position. The objective lens (118) is installed in a lens focus actuator (119). The lens focus actuator (119) is used to adjust the distance between the objective lens (118) and the semiconductor wafer (W).

[0047] The imaging optical system (120) can be constructed using various optical elements. For example, the imaging optical system (120) may include a tube lens (123). Additionally, the imaging optical system (120) may use the objective lens (118) and beam splitter (116) of the illumination optical system (110).

[0048] The objective lens (118) collects light reflected from the semiconductor wafer (W). The light collected by the objective lens (118) passes through the beam splitter (116) and is then focused to the image detector (130) by the tube lens (123).

[0049] The image detector (130) receives reflected light from an alignment mark by illumination and generates an image. The image detector (130) may be a CCD camera or a CMOS camera.

[0050] The controller (200) is coupled to the imaging system (100) so as to be able to communicate via wired or wireless means. The controller (200) may include hardware such as a processor, memory, fixed memory (ROM), a storage device such as a hard disk or SSD, and a wired or wireless communication device. Additionally, it includes a program such as firmware or software installed on a storage medium such as memory, fixed memory, or a storage device.

[0051] A computing device such as an MCU (Micro controller unit), a desktop computer, a laptop computer, a smartphone, or a smart pad can be used as the controller (200).

[0052] The controller (200) of the overlay measuring device (10) may instruct the processor to execute program instructions to perform all or part of the steps of FIG. 4. It is preferable that all steps be directed by the controller (200) so as to minimize human intervention.

[0053] FIG. 4 is a flowchart of a recipe generation method according to an embodiment of the present invention.

[0054] As illustrated in FIG. 4, a recipe generation method according to an embodiment of the present invention includes the steps of obtaining a set of optimal parameter candidates (S1), setting an overlay measurement device with an existing parameter set (S2), positioning an alignment mark within the measurement range of the overlay measurement device (S3), setting an overlay measurement device with a set of optimal parameter candidates (S4), obtaining a new reference alignment mark image (S5), and generating an optimal candidate recipe (S6).

[0055] The alignment mark may be a global alignment mark for aligning the wafer or an overlay mark for aligning between pattern layers formed on the wafer.

[0056] First, the step (S1) of obtaining a set of optimal parameter candidates is described.

[0057] The parameters constituting the optimal parameter candidate set of this step (S1) may include, for example, the wavelength band of the illumination, the numerical aperture value (NA), the focal position, the size and position of the pinhole, etc.

[0058] Figure 5 is a flowchart of an example of the steps for obtaining a set of optimal parameter candidates.

[0059] As illustrated in FIG. 5, the present step (S11) includes the step of selecting a measurement target site (S11), the step of obtaining overlay mark images for each parameter set (S12), the step of calculating quality indicator values ​​for each parameter set (S13), and the step of selecting an optimal parameter candidate set (S14).

[0060] First, the step of selecting at least one measurement target site (S11) is described. This step (S11) is a step of selecting several measurement target sites that can represent the wafer and the process.

[0061] FIG. 6 is a diagram showing measurement sites on a semiconductor wafer marked with dots. An overlay mark is formed at each measurement site. As shown in FIG. 6, multiple overlay marks are formed on a single semiconductor wafer. The overlay marks are formed on the scribe lanes of the semiconductor wafer.

[0062] Although not shown in the image, in the case of a global alignment mark, it is mainly placed near the edge of the wafer.

[0063] In this step (S11), existing measurement results can be analyzed to select a minimum number of representative sites.

[0064] Next, the step (S12) of obtaining overlay mark images for each parameter set is described.

[0065] In this step (S12), first, a parameter set is defined. For example, parameters such as the wavelength band of the illumination, numeric aperture value (NA), focus position, and pinhole size may be included in the parameter set.

[0066] Next, multiple parameter sets having different parameter values ​​are defined by changing the values ​​of the parameters included in the parameter set within an adjustable range.

[0067] Next, after setting the overlay measurement device to the parameter values ​​of the parameter set, capture is taken to acquire one or more overlay mark images. This process is repeated to acquire one or more overlay mark images for each parameter set.

[0068] Next, the step (S13) of calculating quality indicator values ​​for each parameter set is described.

[0069] In this step (S13), the overlay mark images from the previous step (S12) are analyzed. For example, a numerical value of the clarity of the layered structure, the periodicity, repeatability, and symmetry of the grid included in the overlay mark image can be calculated as a quality indicator value.

[0070] The overlay mark image may include a first overlay mark and a second overlay mark formed with different pattern layers. The clarity of the first overlay mark and the second overlay mark in the overlay mark image may differ. This is because there may be a height difference between the first overlay mark and the second overlay mark, and they may be made of different materials. The periodicity, repeatability, and symmetry of the grid may also differ from layer to layer.

[0071] Next, the step (S14) of selecting at least one optimal parameter candidate set is described.

[0072] In this step (S14), at least one optimal parameter candidate set is selected based on the quality indicator values ​​for each parameter set obtained in the previous step (S13).

[0073] This step (S14) can be performed, for example, through Response Surface Methodology. Response Surface Methodology is a method for optimizing multiple quality indicator values ​​by adjusting multiple parameters.

[0074] The relationship between parameters and individual quality indicators can be mathematically modeled using methods such as polynomial regression, and a response surface graph can be plotted using the constructed regression model. The response surface graph visually demonstrates how parameters interact to influence quality indicator values. By analyzing the response surface graph, a set of candidate optimal parameters can be easily selected.

[0075] Next, the step (S2) of setting up an overlay measurement device with an existing parameter set is described.

[0076] This step (S2) is a process of applying a preset set of existing parameters to accurately measure the overlay marks on the wafer.

[0077] In this step (S2), the overlay measuring device loads the data provided in the recipe and the previously stored parameter values, and sets options such as the wavelength band of the illumination of the overlay measuring device, the numeric aperture value (NA), the focus position, and the size and position of the pinhole.

[0078] Using the software of the overlay measurement equipment, a recipe suitable for the corresponding process step can be selected from a list of available recipes. This recipe may include various parameters such as the wavelength band of the illumination, numeric aperture (NA), focal position, size and location of the pinhole, type of alignment mark, and location of the alignment mark.

[0079] Next, the step (S3) of positioning an alignment mark within the measurement range of the overlay measuring device is described.

[0080] In this step (S3), using an existing reference alignment mark image stored in an existing recipe, the alignment mark to be measured is positioned within the measurement range of an overlay measuring device set with an existing parameter set.

[0081] First, the overlay measuring device loads the coordinates of the alignment mark defined in the recipe. Using the coordinates of the alignment mark, the overlay measuring device adjusts the alignment mark so that it falls within the measuring range of the overlay measuring device.

[0082] An existing reference alignment mark image stored in the recipe is loaded into the overlay measurement device. Through a pattern recognition algorithm, the reference alignment mark image is compared with an image captured by the overlay measurement device to detect the position of the alignment mark. The wafer is moved using a stage to accurately position the alignment mark within the measurement range of the overlay measurement device.

[0083] Next, the step (S4) of setting up the overlay measurement device with the optimal parameter candidate set is described.

[0084] In this step (S4), the overlay measurement device is re-set with the optimal parameter candidate set obtained in step S1 instead of the existing parameter set.

[0085] The parameter values ​​of the optimal parameter candidate set are entered into the equipment. This can be done by manually entering them in the software or by loading a pre-saved recipe file.

[0086] Although the wavelength band of the illumination, numeric aperture (NA), focal position, and the size and location of the pinhole of the overlay measurement device are changed, the wafer is not moved, so the alignment mark is accurately positioned within the measurement range of the overlay measurement device.

[0087] Next, the step (S5) of obtaining a new reference alignment mark image is described.

[0088] In this step (S5), an alignment mark is captured using an overlay measuring device set with an optimal parameter candidate set. This alignment mark image becomes the reference alignment mark image of the corresponding optimal parameter candidate set. Since the parameters of the overlay measuring device have been changed, a new reference alignment mark image can be obtained that is similar in shape to the existing reference alignment mark image but has significantly different quality and characteristics.

[0089] For example, if the wavelength of the light becomes shorter, it is advantageous for detecting small patterns or fine details, but the depth of field may be shallow. High aperture values ​​can increase resolution, but the depth of field may be shallow. If the pinhole size becomes smaller, contrast increases and sharp images can be obtained, but the image may become darker and noise may increase.

[0090] Next, the step (S6) of generating the optimal candidate recipe is described.

[0091] In this step (S6), an optimal candidate recipe is generated that includes a set of optimal parameter candidates and a new reference alignment mark image.

[0092] Assign a unique name to the optimal candidate recipe and enter additional metadata (process step, equipment type, wafer type, alignment mark location, etc.).

[0093] The generated optimal candidate recipes are stored in the controller of the overlay measurement equipment or in another database. The optimal candidate recipes include a parameter set and a reference alignment mark image. The stored optimal candidate recipes can be shared across other equipment or process lines using the same process.

[0094] By repeating the steps described above, multiple optimal candidate recipes can be obtained. Then, by using these optimal candidate recipes to acquire and evaluate alignment mark images, the optimal recipe can be found.

[0095] The finally optimized recipe is input into the controller of the overlay measurement equipment and stored in a database so that it can be easily recalled whenever needed.

[0096] If the goal is to generate an optimal recipe for both global alignment and overlay error measurement, steps S3 to S5 are performed on the global alignment mark, and then steps S3 to S5 are performed again on the overlay mark to generate an optimal candidate recipe in which the optimal candidate recipe, the reference alignment mark image for global alignment, and the reference alignment mark image for overlay error measurement are all stored.

[0097] The embodiments described above are merely illustrative of preferred embodiments of the present invention, and the scope of the present invention is not limited to the described embodiments. Various changes, modifications, or substitutions may be made by those skilled in the art within the technical spirit and scope of the claims of the present invention, and such embodiments should be understood to fall within the scope of the present invention.

[0098] [Explanation of the symbol]

[0099] 10: Overlay measuring device

[0100] 100: Imaging System

[0101] 110: Illumination optical system

[0102] 115: Pinhole

[0103] 120: Imaging optical system

[0104] 130: Image detector

[0105] 200: Controller

Claims

1. A method for automatically generating a recipe for an overlay measuring device, a) a step of obtaining a set of optimal parameter candidates, and, b) A step of setting up an overlay measurement device with an existing parameter set, and c) a step of positioning an alignment mark within the measurement range of the overlay measuring device set with an existing parameter set using an existing reference alignment mark image, and d) a step of setting up an overlay measurement device with the above-mentioned optimal parameter candidate set, and e) a step of capturing the alignment mark with an overlay measuring device set with the optimal parameter candidate set to obtain a new reference alignment mark image corresponding to the optimal parameter candidate set, and f) A recipe generation method comprising the step of generating an optimal candidate recipe including the above optimal parameter candidate set and the above new reference alignment mark image.

2. In Paragraph 1, Step a) above is, a-1) A step of selecting at least one measurement target site, and, a-2) A step of obtaining overlay mark images for each parameter set by photographing an overlay mark located at the measurement target site while changing the parameter values ​​of the overlay measuring device, and a-3) A step of analyzing the above overlay mark images to calculate quality indicator values ​​for each parameter set, and a-4) A recipe generation method comprising the step of selecting at least one set of optimal parameter candidates based on quality indicator values ​​for each set of parameters.

3. In Paragraph 2, A recipe generation method in which the above quality indicator value includes at least one of the clarity of the layered structure included in the overlay mark image, the periodicity, repeatability, and symmetry of the grid.

4. In Paragraph 2, The above step a-4) is a recipe generation method in which the set of optimal parameter candidates is selected through Response Surface Methodology.

5. In Paragraph 1, A recipe generation method in which the above alignment mark is a global alignment mark for aligning a wafer or an overlay mark for aligning between pattern layers formed on a wafer.

6. An overlay measurement device comprising an imaging system configured to acquire an alignment mark image and a controller communically coupled to the imaging system, The above controller includes at least one memory containing instructions and a processor configured to execute the instructions contained in the at least one memory, and the processor executes the instructions, a) a step of obtaining a set of optimal parameter candidates, and, b) A step of setting up an overlay measurement device with an existing parameter set, and c) a step of positioning an alignment mark within the measurement range of the overlay measuring device set with an existing parameter set using an existing reference alignment mark image, and d) a step of setting up an overlay measurement device with the above-mentioned optimal parameter candidate set, and e) a step of capturing the alignment mark with an overlay measuring device set with the optimal parameter candidate set to obtain a new reference alignment mark image corresponding to the optimal parameter candidate set, and f) An overlay measuring device that performs the step of generating an optimal candidate recipe including the above optimal parameter candidate set and the above new reference alignment mark image.

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