Method and device for overlay measurement

Abstract

A method comprises receiving an image formed in a metrology device, wherein the image comprises at least the resulting effects of at least two diffraction orders, and processing the image, wherein the processing comprises at least a filtering step, such as Fourier filtering. The process of applying the filter can also be obtained by placing an aperture in the detection branch of the metrology device.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 62 / 787,191, filed on December 31, 2018, the entire contents of which are incorporated herein by reference.

[0003] A lithographic apparatus is a machine that applies a desired pattern to a substrate (usually to a target portion of a substrate). A lithographic apparatus can be used, for example, in the manufacture of an integrated circuit (IC). In that case, a pattern forming device (which is alternatively referred to as a mask or reticle) can be used to produce a circuit pattern to be formed on a single layer of the IC. This pattern can be transferred to a target portion (e.g., including a portion of a die, a die, or several dies) on a substrate (e.g., a silicon wafer). The transfer of a pattern is usually performed via imaging onto a radiation-sensitive material (resist) layer disposed on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are continuously patterned.

[0004] Important aspects of implementing a patterning process (i.e., a process that produces a device or other structure that involves patterning (such as lithographic exposure or imprinting), which may typically include one or more associated processing steps such as developing a resist, etching, etc.) include: developing the process itself; setting up the process for monitoring and control and then actually monitoring and controlling the process itself. Given a configuration of the principles of the patterning process, such as patterned device pattern, resist type, post-lithographic process steps (such as developing, etching, etc.), it is desirable to set up equipment during the patterning process for transferring the pattern onto a substrate, develop one or more metrology targets to monitor the process, set up a metrology process to measure the metrology targets and then implement process monitoring and / or control of the process based on the measurements.

[0005] Thus, during the patterning process, it is desirable to determine (e.g., measure, simulate using one or more models that model one or more aspects of the patterning process, etc.) one or more parameters of interest, such as the critical dimension (CD) of the structure, the overlay error between successive layers formed in or on the substrate (i.e., undesirable and unintentional misalignment of successive layers), etc.

[0006] It is desirable to determine such one or more parameters of interest of a structure produced by a patterning process, and to use the one or more parameters of interest for design, control, and / or monitoring related to the patterning process, e.g., for process design, control, and / or verification. The determined one or more parameters of interest of the patterned structure may be used for patterning process design, correction, and / or verification, defect detection or classification, yield estimation, and / or process control.

[0007] Therefore, during the patterning process, it is desirable to frequently measure the resulting structure, for example for process control and verification. Various tools for making such measurements are well known, including scanning electron microscopes, which are often used to measure critical dimensions (CDs), and specialized tools to measure overlay (measuring the alignment accuracy of two layers in a device). Overlay can be described in terms of the degree of misalignment between two layers, for example a reference to a measured overlay of 1 nm can describe a situation where the two layers are misaligned by 1 nm.

[0008] Various forms of inspection equipment (e.g., metrology devices) have been developed for use in the field of lithography. For example, a scatterometry device directs a radiation beam onto a target and measures one or more properties of the redirected (e.g., scattered) radiation to obtain a "spectrum" that can be used to determine properties of interest of the target, such as intensity at a single reflection angle as a function of wavelength, intensity at one or more wavelengths as a function of reflection angle, or polarization as a function of reflection angle. Determination of the properties of interest can be performed by various techniques: for example, reconstruction of the target by iterative methods such as rigorous coupled wave analysis or finite element methods; library searching; and principal component analysis.

[0009] Another technique involves blocking the zero diffraction order (corresponding to specular reflection) and processing only higher orders. Examples of such measurements can be found in PCT Patent Application Publication Nos. WO 2009 / 078708 and WO 2009 / 106279, which are incorporated herein by reference in their entirety. Further developments of the techniques have been described in U.S. Patent Application Publications Nos. US 2011-0027704, US 2011-0043791, and US2012-0242940, each of which is incorporated herein by reference in its entirety. Such diffraction-based techniques are often used to measure overlap. The target of the technique may be smaller than the illumination spot and may be surrounded by product structures on the substrate. The target may include multiple periodic structures that may be measured in one image. In a specific form of such a measurement technique, overlap measurements are obtained by measuring the target twice under certain conditions, while rotating the target or changing the illumination mode or imaging mode to obtain -1 diffraction order intensity and +1 diffraction order intensity, respectively. The intensity asymmetry (comparison of the intensities of these diffraction orders) about a given target provides a measure of the target asymmetry (ie the asymmetry in the target). This asymmetry in the target can be used as an indicator of overlay error.

[0010] Therefore, as described, during the manufacturing process, it is necessary to inspect the manufactured structure and / or measure one or more characteristics of the manufactured structure. Suitable inspection and measurement devices are known in the art. One type of measurement device among the known measurement devices is a scatterometer and, for example, a dark field scatterometer. U.S. Patent Application Publication US 2016 / 0161864, U.S. Patent Application Publication US 2010 / 0328655, and U.S. Patent Application Publication US 2006 / 0066855 discuss embodiments of photolithography equipment and embodiments of scatterometers. The cited documents are incorporated herein by reference in their entirety.

[0011] Electronic devices such as integrated circuits are often manufactured by means of a manufacturing process in which layers are formed one above the other on a substrate by means of several process steps. One of the process steps may be photolithography, which may use electromagnetic radiation in the deep ultraviolet (DUV) spectral range or in the extreme ultraviolet (EUV) spectral range. The substrate is often a silicon wafer. The smallest size of the manufactured structures is in the nanometer range.

[0012] Figure 1 A schematic diagram of a dark field scatterometer as described above is depicted, and the image formed if the imaging sensor is placed in the image plane or pupil plane of the scatterometer. The image formed in the image plane is depicted in element 100, where the image plane is element 102. The image formed in the pupil plane is depicted in element 101. Element 103 is an overlapping grating, where a relative offset is formed between the top and bottom gratings, that is, there is an overlap between the two layers. Element 104 depicts the radiation incident on the grating and the resulting 0th order or specular scattered radiation. In a dark field scatterometer, this radiation is blocked by the design of the device, such as by using an aperture in the illumination branch, as described in the previously cited prior art. Elements 105 and 106 depict the diffraction orders produced by scattering of the incident branch of 104 radiation on the target 103. 105 depicts the negative orders, and 106 depicts the positive orders.

[0013] In diffraction based metrology methods and apparatus, there is a relationship between the wavelength of the light, the pitch of the grating on the wafer and the NA (numerical aperture) of the optical system (in this case, the metrology tool or scatterometer). If the ratio between wavelength and pitch is less than the NA of the optical system, which is multiplied by a constant, the image will not be able to resolve structures on the target. However, if the ratio is greater than the NA multiplied by a constant (which is 1 in most cases), the measured image will resolve structures present on the wafer and the structures become visible. In a typical mode of operation, a dark field scatterometer cannot resolve structures / targets on the wafer and the metrology method relies on measuring the average intensity of the image obtained. This method is well described in the art and in the previously cited patent applications. In this typical mode of operation, the pitch of the structure is comparable to the wavelength of the light.

[0014] When the target below (such as Figure 1 Problems arise when the pitch of the elements 103 in the pupil plane becomes much larger than the wavelength of the incident radiation. In this case, as depicted by element 100, multiple diffraction orders are available in the pupil plane and all contribute to the image formation in the image plane, as shown in FIG. Figure 1 100. These large pitch targets (generally large as defined with respect to the wavelength of light used in the metrology equipment) occur, for example, in the metrology of 3D-NAND structures, where the pitch of the metrology targets is in the micrometer range due to limitations imposed by specific processing conditions, where the wavelength of light remains within the optical band. Such an abundance of diffraction orders leads to complex interference patterns, as depicted in element 100, which are difficult to eliminate when using prior art overlap extraction methods (which rely on smooth images as obtained when the wavelength and the pitch of the grating are comparable).

[0015] An object of the present invention is to provide a method that allows the use of prior art overlay measurements in a frequency band where the wavelength of the radiation is smaller than the pitch of the measurement target. The method comprises: obtaining an image in the image plane of the measurement detection branch, for example when the imaging sensor is placed in the image plane; and filtering the image of the contribution due to the complex interference pattern of multiple non-zero diffraction orders. In an embodiment, the filter is a digital filter. In an embodiment, the digital filter is a Fourier filter, in which only low-frequency components in the image are obtained. In an embodiment, the filter is a Fourier filter, which is applied to a composite image obtained as a difference between images formed by positive and negative orders. In an embodiment, before obtaining an asymmetric image as a difference between images formed by negative and positive orders, an alignment step is performed between the images obtained from the negative and positive orders. The prior art dark field measurement method can be further applied to the asymmetric image obtained after digital filtering.

[0016] In an embodiment, the method comprises: Figure 3 Element 300 is as follows Figure 1 Element 300 may be an asymmetric image obtained after an alignment step between the images formed by the positive and negative orders and a further subtraction of the aligned image. Step 301 depicts a filtering step applied to element 300. Element 302 is a sketch representation of the resulting image. Element 302 is an ideal representation of the obtained signal, as it is desired in practical applications that sharp corners may be rounded and possible nuisance signals still exist in the resulting filtered image.

[0017] In another embodiment, filtering of high diffraction orders is obtained by placing an aperture in the detection branch of the metrology device. Since the ratio between the wavelength of the light and the pitch of the grating is known, and the NA of the system is further known, the aperture can be designed to have a light transmission portion that only allows a single diffraction order. In an embodiment, the diffraction orders are the +1 and -1 diffraction orders. In another embodiment, the diffraction orders are the +2 and -2 diffraction orders. Depending on the type of metrology process and metrology application, further combinations of single orders can be envisioned. Figure 2 Such apertures in elements 201 and 202 are depicted.

[0018] Although much of the discussion has focused on target structures as metrology targets that are specifically designed and formed for the purpose of measurement, in other embodiments, the target can be a functional part of a device formed on a substrate. Many devices have a regular periodic structure similar to a grating. As used herein, the terms "target," "grating," or "periodic structure" of a target need not specifically provide a suitable structure for the measurement being performed.

[0019] In an embodiment, the target can be achieved using a pattern forming device (such as a reticle or mask) designed to produce a target on a substrate (e.g., to produce a pattern image for projection onto a resist layer, the patterned resist layer being used to form the target using subsequent processing steps such as deposition, etching, etc.).

[0020] In conjunction with the physical structure of the target as implemented on a substrate and a pattern forming device (such as a reticle or mask), an embodiment may include a computer program containing one or more sequences of machine-readable instructions and / or functional data describing a target design, describing a method of generating a target on a substrate, describing a method of measuring a target on a substrate, and / or describing a method of analyzing measurements to obtain information about a patterning process (e.g., a lithography process, an etching process, etc.). Such a computer program can be executed in a processing device or a measurement or inspection device of, for example, a lithography device or a lithography unit, or on a stand-alone computer. A data storage medium (e.g., a semiconductor memory, a magnetic disk, or an optical disk) may also be provided, in which such a computer program is stored. If an existing measurement or inspection device is already in production and / or in use, an embodiment may be implemented by providing an updated computer program product for causing a processor to perform one or more of the methods described herein. The process may optionally be arranged to control the device, etc. to perform the method as described herein. The process may update the lithography and / or measurement options for measurement of the substrate. The process may be arranged to control (directly or indirectly) the lithography device for patterning and processing the substrate.

[0021] Embodiments of the present invention may take the form of a computer program comprising one or more sequences of machine-readable instructions describing a method as disclosed herein, or a data storage medium (e.g., a semiconductor memory, a magnetic disk, or an optical disk) in which such a computer program is stored. Furthermore, the machine-readable instructions may be embodied in two or more computer programs. The two or more computer programs may be stored on one or more different memories and / or data storage media.

[0022] One or more aspects disclosed herein can be implemented in a control system. Any control system described herein can be operated individually or in combination when one or more computer programs are read by one or more computer processors located in at least one component of the device. Each of the control systems can have any suitable configuration for receiving, processing and sending signals or in combination. One or more processors are configured to communicate with at least one control system in the control system. For example, each control system may include one or more processors for executing a computer program, and the computer program includes machine-readable instructions for the method described above. The control system may include a data storage medium for storing such a computer program, and / or hardware for receiving such a medium. Therefore, the control system can operate according to the machine-readable instructions of one or more computer programs.

[0023] Although specific reference may be made above to the use of embodiments in the context of optical lithography, it will be appreciated that embodiments of the invention may be used in other applications. For example, embodiments may relate to imprint lithography. In imprint lithography, the topography in a patterning device defines the pattern produced on a substrate. The configuration of the patterning device may be pressed into a resist layer supplied to a substrate, on which the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist, leaving a pattern therein. In addition, the embodiments herein may be used with any process that produces a structure and may therefore be used with, for example, other material removal processes or with an additive process.

[0024] The terms "radiation" and "beam" as used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5 to 20 nm), as well as particle beams, such as ion beams or electron beams.

[0025] Unless otherwise specifically stated, as is apparent from the discussion, it should be understood that throughout this specification, discussions utilizing terms such as "processing," "computing," "calculating," "determining," etc. may refer to actions or processes of a specific apparatus such as a special purpose computer or similar special purpose electronic processing / computing device.

[0026] It should be understood that the embodiments and drawings are not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0027] In view of the embodiments, those skilled in the art will understand the modification and alternative embodiments of various aspects of the present invention. Therefore, the embodiments and the accompanying drawings should be understood to be illustrative only and for the purpose of teaching those skilled in the art to carry out the general mode of the present invention. It should be understood that the forms of the present invention shown and described herein should be regarded as examples of embodiments. Elements and materials can replace the elements and materials illustrated and described herein, parts and processes can be reversed or omitted, certain features can be utilized independently, and the features of embodiments or embodiments can be combined, and those skilled in the art will understand all of these after obtaining the benefits of embodiments of the present invention. Changes can be made to the elements described herein without departing from the spirit and scope of the present invention as described in the appended claims. The titles used herein are only for organizational purposes and are not intended to limit the scope of the embodiments.

[0028] As used throughout this application, the word "may" is used in a permissive sense (i.e., meaning may) rather than in a mandatory sense (i.e., meaning must). The words "include, including, and includes," and the like mean including, but not limited to. As used throughout this application, the singular forms "a," "an," and "the" include plural referents unless the content clearly indicates otherwise. Thus, for example, reference to "an element" includes a combination of two or more elements, although other terms and phrases, such as "one or more," may be used with respect to one or more elements. Unless otherwise indicated, the term "or" is non-exclusive, i.e., covers both "and" and "or." Terms describing conditional relationships, such as "in response to X, and Y", "after X, then Y", "if X, then Y", "when X, Y", etc., cover causal relationships where the antecedent is a necessary causal condition, the antecedent is a sufficient causal condition, or the antecedent is a contributing causal condition to the result, such as "after condition Y is obtained, state X occurs" is common to "only after Y, then X occurs" and "after Y and Z, then X occurs". Such conditional relationships are not limited to results obtained by immediately following the antecedent, because some results can be delayed, and in conditional statements, the antecedent is connected to its results, for example, the antecedent is related to the probability of the occurrence of the result. In addition, unless otherwise indicated, the statement that a value or action is "based on" another condition or value covers both the case where the condition or value is the only factor and the case where the condition or value is one factor among multiple factors. Unless otherwise indicated, the statement that "each" instance of a certain aggregate has a certain property should not be interpreted as excluding the case where some otherwise identical or similar members of the larger aggregate do not have the said property (i.e., each does not necessarily mean every one).

[0029] In the event that certain U.S. patents, U.S. patent applications, or other materials (e.g., articles) have been incorporated by reference, the text of such U.S. patents, U.S. patent applications, and other materials is incorporated by reference only to the extent that there is no conflict between such materials and the statements and drawings set forth herein. In the event of such a conflict, any such conflicting text in such incorporated by reference U.S. patents, U.S. patent applications, and other materials is not specifically incorporated by reference herein.

[0030] The foregoing description of specific embodiments discloses the general nature of embodiments of the present invention, so that others can easily modify and / or adapt such specific embodiments for various applications by applying knowledge understood by those skilled in the art without departing from the general concept of the present invention, without the need for excessive experimentation. Therefore, based on the teachings and guidance presented herein, such adaptations and modifications are intended to be within the meaning and scope of the equivalents of the disclosed embodiments. It should be understood that the phrases or terms herein are for purposes of, for example, description rather than limitation, so that the terms or phrases of this specification will be interpreted by those skilled in the art in view of the teachings and guidance.

[0031] The above description is intended to be illustrative rather than restrictive. Therefore, it will be appreciated by those skilled in the art that the invention as described may be modified without departing from the scope of the claims set forth below, and that the breadth and scope of the invention should not be limited by any of the exemplary embodiments described above, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A method for performing overlapping measurements in a frequency band where the wavelength of radiation is smaller than the pitch of a measurement target, comprising: receiving an image formed in a metrology device, wherein the image includes at least effects produced by at least two non-zero diffraction orders, and processing the image, wherein the processing comprises at least a filtering step, The non-zero diffraction order comprises a positive order and a negative order, and the image is an asymmetric image obtained after an alignment step between images formed by the positive order and the negative order and a further subtraction of the aligned image.

2. The method according to claim 1, wherein: The filtering step is a digital filtering step.

3. The method according to claim 1 or 2, wherein: The measuring device comprises an aperture, wherein the aperture comprises: An element comprising a radiation transmissive portion, wherein the radiation transmissive portion transmits a single diffraction order.

4. A measurement device for use in the method according to any one of claims 1 to 3, comprising: An aperture located in a detection branch of the measurement device.

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