A method and system for measuring optical path uniformity based on a vision system

Abstract

The application discloses a kind of light path uniformity measurement method and system based on vision system, belong to integrated circuit processing and manufacturing technical field.The system includes industrial camera, microscope lens and reflector;Among them, microscope lens is telecentric lens;By being arranged between spatial light modulator component and projection objective lens of photoetching machine of light path uniformity measurement system, the light spot formed by the light emitted by photoetching machine light source passes through reflector, and then enters the sensor surface of industrial camera finally imaged to microscope lens, obtains the image of light spot, calculates the global uniformity feature and local uniformity feature of the light spot image, and then obtains the uniformity value of the light spot image, the uniformity value calculated by the method can participate in the analysis of uniformity from the overall image, and by adding local features, the rich data information contained in local image is utilized, so that the final calculation result can more comprehensively express the uniformity performance of image.

Description

Technical Field

[0001] This invention relates to a method and system for measuring optical path uniformity based on a vision system, belonging to the field of integrated circuit processing and manufacturing technology. Background Technology

[0002] Integrated circuit manufacturing is a technology closely related to specialized equipment, commonly known as "one generation of equipment, one generation of process, one generation of product." Among the many processes and equipment required for integrated circuit production, photolithography technology is the core representative of the level of integrated circuit manufacturing technology. The resolution and minimum linewidth of a generation of photolithography machines directly represent the technology node of a generation of integrated circuits.

[0003] As the core of lithography equipment, the projection exposure system directly determines the minimum linewidth, precision, and quality of the lithography process. The projection exposure system requires evaluation based on various indicators, such as depth of focus, minimum resolution, and linewidth consistency. Depth of focus and minimum resolution are generally determined by the imaging lens, while linewidth consistency is determined by the uniformity of the light spot. In a projection exposure system, the illumination path is positioned between the light source and the spatial light modulator, converting the light emitted from the light source into parallel light to provide the spatial light modulator with an illumination light field of specific intensity distribution, i.e., a light spot of a certain size and uniformity. For lithography machines with high linewidth consistency requirements, the uniformity of the light spot is generally required to be >90%–95%. Therefore, accurate measurement of the light spot uniformity is necessary for adjustment and compensation.

[0004] Because lithography machines have extremely high requirements for spot uniformity, to ensure energy uniformity, the energy at each position of the spot needs to be tested, confirmed, and adjusted until the uniformity requirements are met. For conventional optical paths, uniformity testing typically uses a power meter. The spot is evenly divided into 10, 20, or even more equal parts, and the energy of each segmented spot is measured. Finally, the data is processed, and the uniformity is calculated using the formula Uniformity = (Imax - Imin) / (Imax + Imin). However, power meters have low resolution, and measurements are inaccurate or even undetectable when the spot size is too small (high-resolution optical paths typically have low lens magnification, usually less than 1x, resulting in spot sizes of less than 5mm; after segmentation, each spot is only a few hundred micrometers, which the power meter cannot measure). For the small spot size of high-resolution laser direct-write exposure machines, power meters cannot provide accurate testing due to large errors, poor repeatability, and are essentially ineffective for measurement. For example, high-resolution lithography machines typically output power in the milliwatt range (100mW-1mW). Measuring by dividing the light spot into segments significantly reduces the energy within each spot. Due to limitations in power measurement range and accuracy, this method is time-consuming and inconvenient. Furthermore, using conventional low-energy optical power timing systems is susceptible to environmental and operational influences, leading to additional environmental and human errors. Therefore, the aforementioned testing methods are time-consuming, labor-intensive, and lack guaranteed accuracy. Summary of the Invention

[0005] To achieve accurate calculation of the optical path uniformity of lithography equipment, this invention provides an optical path uniformity measurement method based on a vision system, the method comprising:

[0006] Step S1: Obtain an image of the light spot generated by the illumination optical path in the projection exposure system, denoted as light spot image I;

[0007] Step S2: Calculate the global uniformity feature GlobalU of the light spot image I;

[0008] Step S3: Calculate the local uniformity feature LocalU of the light spot image I;

[0009] Step S4: Calculate the uniformity U = GlobalU + LocalU of the spot image I based on the global uniformity feature GlobalU and the local uniformity feature LocalU.

[0010] Optionally, step S2 includes:

[0011] Let the length and width of the light spot image I be Width and Height, respectively. Calculate the global uniformity feature GlobalU of the light spot image I according to equation (1):

[0012]

[0013] in,

[0014]

[0015] I(i,j) represents the pixel grayscale value in the i-th row and j-th column of the spot image I. avg is the mean value of the grayscale image I of the light spot image.

[0016] Optionally, step S3 includes:

[0017] Step S3.1: Divide the light spot image I into M and N equal parts along the horizontal and vertical directions, respectively, to divide the light spot image I into M*N sub-region images;

[0018] Step S3.2: Calculate the similarity value between each sub-region image and the other M*N-1 sub-region images;

[0019] Step S3.3: Calculate the similarity values ​​between each sub-region image and other sub-region images to obtain a similarity array with a data size of M*N. Calculate the average value of the array as the local uniformity feature LocalU of the spot image I.

[0020] Optionally, in step S3.3, the similarity value between each sub-region image and the other M*N-1 sub-region images is represented by the image cosine similarity, hash value similarity, structural similarity, and image histogram similarity.

[0021] Optionally, when using cosine similarity to represent the similarity between each sub-region image and the other M*N-1 sub-region images, the calculation process for the similarity value between each sub-region image and the other sub-region images includes:

[0022] Step S3.3.1: Convert the grayscale arrays of the sub-region images img1 and img2, which have lengths and widths of w and h respectively, so that the two-dimensional arrays of the two sub-region images are each converted into a one-dimensional array A and B of size 1*(w*h);

[0023] Step S3.3.2, calculate the similarity value between the two images according to equation (3):

[0024]

[0025] Among them, A k B represents the k-th element in array A. k · represents the k-th element in array B, and · represents the product symbol.

[0026] Optionally, in step S1, an optical path uniformity measurement system based on a vision system is used to acquire an image of the light spot generated by the illumination optical path in the projection exposure system. The optical path uniformity measurement system based on a vision system includes an industrial camera, a microscope head, and a reflector. The microscope head is a telecentric lens. When acquiring the image of the light spot, the reflector is placed between the spatial light modulator assembly and the projection lens of the lithography machine, so that the light spot formed by the light emitted by the light source of the lithography machine passes through the reflector and then enters the microscope head to finally image onto the sensor surface of the industrial camera, and the industrial camera obtains an image of the light spot.

[0027] This application also provides a vision-based optical path uniformity measurement system, which is installed between the spatial light modulator assembly and the projection lens of a lithography machine. The system includes an industrial camera, a microscope lens, and a reflector; wherein the microscope lens is a telecentric lens; when acquiring an image of a light spot, the reflector is positioned below the spatial light modulator assembly, so that the light spot formed by the light emitted by the lithography machine's light source passes through the reflector, enters the microscope lens, and is finally imaged onto the sensor surface of the industrial camera, thus obtaining an image of the light spot for the industrial camera.

[0028] Optionally, the industrial camera is a CMOS camera with a pixel count greater than 1 million.

[0029] The beneficial effects of this invention are:

[0030] The method acquires images of light spots generated by the illumination optical path in the projection exposure system through an optical path uniformity measurement system, calculates the global and local uniformity features of the light spot image, and then obtains the uniformity value of the light spot image. The uniformity value calculated by this method can participate in the uniformity analysis from the perspective of the overall image, and by adding local features, it can utilize the rich data information contained in the local image, so that the final calculation result can more comprehensively express the uniformity performance of the image. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1This is a schematic diagram of the position of a vision-based optical path uniformity measurement system installed in a lithography machine according to an embodiment of the present invention. In this diagram, 4-spatial light modulator assembly and 6-projection lens are components of the lithography machine, and 1-industrial camera, 2-microscope head, 3-reflector and 5-reflector base are components of the optical path uniformity measurement system.

[0033] Figure 2 This is a flowchart of a vision system-based optical path uniformity measurement method provided in one embodiment of the present invention.

[0034] Figure 3 This is a schematic diagram of dividing the original spot image I into M*N sub-region images in one embodiment of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0036] Explanation of technical terms:

[0037] 1. Illumination Uniformity: This refers to the degree of difference in illumination distribution between a specific area and its neighboring areas within the field of view (e.g., between adjacent areas of a work surface). The smaller the difference, the better; the larger the difference, the worse. Holoor, an Israeli company, defines light spot uniformity in terms of contrast ratio.

[0038] Uniformity=(Imax-Imin) / (Imax+Imin)

[0039] 2. Laser Power Meter: This is an instrument used to measure the power of continuous laser light or the average power of pulsed laser light over a certain period of time. For example, laser energy meters are commonly used to detect the single-shot energy of repetitive pulsed lasers and the energy of single-pulse lasers. Alternatively, thermopile-type laser power meters convert light energy into heat through a thermopile structure, and then into an electrical signal output. Calibration is then used to accurately measure the laser power.

[0040] 3. Telecentric Lens: A telecentric lens is a lens that maintains a constant magnification of the image within a certain object distance range. This is crucial for applications where the objects being measured are not on the same plane. Due to its unique parallel optical path design, telecentric lenses have always been favored in machine vision applications where high distortion accuracy is critical.

[0041] 4. Industrial Camera: The industrial camera is a key component of a machine vision system. Its most essential function is to convert light signals into ordered electrical signals. Selecting a suitable camera is also an important part of the machine vision system design. The choice of camera not only directly determines the resolution and image quality of the acquired images, but also is directly related to the operating mode of the entire system. The industrial camera selected in this application is a CMOS camera with a pixel count greater than 1 million.

[0042] Example 1:

[0043] This embodiment provides a vision-based optical path uniformity measurement system and method, see [link to documentation]. Figure 1 The optical path uniformity measurement system is installed between the spatial light modulator assembly 4 and the projection lens 6 of the lithography machine. The system includes an industrial camera 1, a microscope head 2, and a reflector 3. The reflector 3 is mounted on a reflector base 5, located above the projection lens 6, so that the light spot formed by the light emitted from the lithography machine's light source passes through the reflector, enters the microscope head 2, and is finally imaged onto the sensor surface of the industrial camera 1. The industrial camera 1 obtains an image of the light spot. The optical path uniformity of the lithography equipment is evaluated based on the uniformity of this light spot. Please refer to [reference needed]. Figure 2 The uniformity of the light spot image is calculated using the following method:

[0044] Step 1: Let the length and width of the spot image I obtained by the industrial camera be Width and Height, respectively. Calculate the global uniformity feature GlobalU of the spot image I according to the following formula:

[0045]

[0046] in,

[0047]

[0048] I(i,j) represents the pixel grayscale value in the i-th row and j-th column of the spot image I. avg is the mean value of the grayscale image I of the light spot image.

[0049] Step 2: Calculate the local uniformity feature LocalU of the light spot image I;

[0050] Step 2.1: Divide the original light spot image I into M*N sub-region images along the horizontal and vertical axes, respectively. Figure 3 As shown;

[0051] Step 2.2 involves iterating through each sub-region image and calculating the image similarity pairwise with the remaining M*N-1 sub-region images. Each sub-region image yields M*N-1 similarity values, which are then averaged. A higher average similarity between a sub-region image and other sub-region images indicates greater similarity and a more similar distribution of grayscale values, signifying better local uniformity of the image. The similarity between two sub-region images can be calculated using cosine similarity, hash value, structural similarity, and the image's histogram.

[0052] The calculation method uses cosine similarity.

[0053] This embodiment uses cosine similarity to represent the similarity between two entities as an example for explanation:

[0054] First, the sub-region images img1 and img2, with lengths and widths of w and h respectively, are converted into grayscale arrays. The two-dimensional arrays of the two sub-region images are each converted into a one-dimensional array A and B of size 1*(w*h). Then, the similarity value between the two images is calculated according to formula (3). The specific calculation formula is as follows:

[0055]

[0056] Among them, A k B represents the k-th element in array A. k · represents the k-th element in array B, and · represents the product symbol.

[0057] Step 2.3: Calculate the similarity value between each sub-region image and other sub-region images to obtain a similarity array with a data size of M*N. Calculate the average value of this array as the local uniformity feature LocalU of the spot image I.

[0058] Step 3: Calculate the uniformity U = GlobalU + LocalU of the spot image I based on the global uniformity feature GlobalU and the local uniformity feature LocalU.

[0059] The uniformity calculation of the light spot in this application method is determined by both global uniformity features and local uniformity features. The uniformity value calculated by this method can participate in the uniformity analysis from the perspective of the overall image, and by adding local features, the rich data information contained in the local image can be utilized, so that the final calculation result can more comprehensively express the uniformity performance of the image.

[0060] Some steps in the embodiments of the present invention can be implemented using software, and the corresponding software program can be stored in a readable storage medium, such as an optical disc or a hard disk.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for measuring the uniformity of optical paths based on a vision system, characterized in that, The method includes: Step S1: Obtain an image of the light spot generated by the illumination optical path in the projection exposure system, denoted as light spot image I; Step S2: Calculate the global uniformity feature GlobalU of the light spot image I; Step S3: Calculate the local uniformity feature LocalU of the light spot image I; Step S4: Calculate the uniformity U of the light spot image I based on the global uniformity feature GlobalU and the local uniformity feature LocalU. Step S2 includes: Let the length and width of the light spot image I be divided into Width and Height. Calculate the global uniformity feature GlobalU of the light spot image I according to equation (1): in, I(i,j) represents the pixel grayscale value in the i-th row and j-th column of the spot image I. avg The mean value of the grayscale image I of the light spot image; Step S3 includes: Step S3.1: Divide the light spot image I into M and N equal parts along the horizontal and vertical directions, respectively, to divide the light spot image I into M*N sub-region images; Step S3.2: Calculate the similarity value between each sub-region image and the other M*N-1 sub-region images; Step S3.3: Calculate the similarity values ​​between each sub-region image and other sub-region images to obtain a similarity array with a data size of M*N. Calculate the average value of the array as the local uniformity feature LocalU of the spot image I.

2. The method according to claim 1, characterized in that, In step S3.3, the similarity value between each sub-region image and the other M*N-1 sub-region images is represented by the image cosine similarity, hash value similarity, structural similarity, and image histogram similarity.

3. The method according to claim 2, characterized in that, When using cosine similarity to represent the similarity between each sub-region image and the other M*N-1 sub-region images, the calculation process for the similarity value between each sub-region image and the other sub-region images includes: Step S3.3.1: Convert the grayscale arrays of the sub-region images img1 and img2, which have lengths and widths of w and h respectively, so that the two-dimensional arrays of the two sub-region images are each converted into a one-dimensional array A and B of size 1*(w*h); Step S3.3.2, calculate the similarity value between the two images according to equation (3): Among them, A k B represents the k-th element in array A. k This represents the k-th element in array B, and · represents the product symbol.

4. The method according to claim 3, characterized in that, In step S1, a vision-based optical path uniformity measurement system is used to acquire an image of the light spot generated by the illumination optical path in the projection exposure system. The vision-based optical path uniformity measurement system includes an industrial camera, a microscope lens, and a reflector. The microscope lens is a telecentric lens. When acquiring the image of the light spot, the reflector is placed between the spatial light modulator assembly and the projection lens of the lithography machine, so that the light spot formed by the light emitted by the lithography machine light source passes through the reflector and then enters the microscope lens to finally image onto the sensor surface of the industrial camera, and the industrial camera obtains an image of the light spot.

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