OCD measurement method based on 3D model relation

Abstract

The invention provides an OCD measurement method based on a 3D model relation, and the method comprises the steps: collecting plane measurement results of a 3D measurement object when a microscope is at different heights, and enabling each plane measurement result to correspond to a picture taking sequence number; establishing a 3D model relationship among the plane measurement result, the image taking sequence number and the 3D measurement object; and calculating the optical critical dimension of the 3D measurement object according to the plane measurement result, the image taking sequence number and the 3D model relationship of the 3D measurement object. The method has the key points that (1) a mode of constructing a 3D model by 2D imaging at different heights is simply adopted; (2) performing data fusion by using different expression characteristics of the measured object under the G and B color lights; and (3) deducing the interested key size by using the convergence and fluctuation rule of the data. The method has the advantages that through verification of a large amount of data, the method is good in stability and accuracy and high in CDSEM matching degree.

Description

Technical Field

[0001] The present invention relates to the technical field of wafers and display panels, and in particular to an OCD measurement method based on a 3D model relationship. Background Art

[0002] In the complex process environment of multi-layer stacking, 3D shapes, and film thickness changes, the following problems arise when using plane measurement methods:

[0003] (1) Plane microscopes cannot stably focus on a certain layer or position;

[0004] (2) At sensitive locations, the focus height changes slightly, resulting in large differences in measured values;

[0005] (3) It is impossible to determine at which height the measurement is correct.

[0006] The above problems mean that the 2D measurement method has poor measurement stability in 3D environments, its accuracy cannot be guaranteed, and its credibility is not high.

[0007] With the development of the semiconductor and display panel industries, the manufacturing process of integrated circuits has been continuously improved and the process has become more and more complex. In order to ensure the quality of the process, precise monitoring is required during the manufacturing process to control the quality and adjust the process in time. OCD (optical critical dimension) measurement is a very important monitoring method. For processes with thinner or flat films, 2D measurement methods are generally used. For processes with thicker films or 3D shapes, 2D measurement methods cannot meet the needs and cannot be measured accurately and stably, so more accurate, stable and efficient 3D measurement methods are needed to deal with it.

[0008] The existing technologies generally include: (1) using multi-dimensional acquisition, which requires the integration of multiple collectors, data acquisition at different angles and orientations, and complex fitting of the data. Only when a complete three-dimensional stereo image is constructed can OCD measurement be performed. This method has a complex structure and is cumbersome. (2) SEM REVIEW machines can perform relatively accurate measurements, but generally only support the measurement requirements of one shot and one point, and cannot perform large-scale measurements. In addition, the measurement speed is relatively slow. This method needs to be improved before it can be applied, and it is also relatively expensive.

[0009] Existing 2D and 3D measurement methods have the following disadvantages when facing practical engineering problems:

[0010] 1. In the complex 3D process environment with multi-layer stacking, 3D shapes, and film thickness changes, the 2D measurement method cannot accurately measure OCD and has poor stability;

[0011] 2. The existing 3D measurement solutions have complex structures, complicated methods and high costs;

[0012] 3. Among the existing 3D measurement methods, the measurement speed is relatively slow, and the measurement precision, accuracy and stability need to be verified. Summary of the invention

[0013] The purpose of the present invention is to use 3D technology to simply, cost-effectively and efficiently solve the problem of unstable and unreliable measurement results faced by existing 2D measurement methods in a 3D measurement environment, while being able to accurately and stably measure the OCD of a 3D model.

[0014] The key points of the present invention are: (1) simply using 2D imaging at different heights to construct a 3D model; (2) using the different performance characteristics of the measured object under G and B color light to perform data fusion; and (3) using the convergence and fluctuation laws of the data to infer the key dimensions of interest.

[0015] Specifically, the present invention provides an OCD measurement method based on a 3D model relationship, comprising:

[0016] Collect the plane measurement results of the 3D measurement object when the microscope is at different heights, and each plane measurement result corresponds to a map acquisition sequence number;

[0017] Establish the 3D model relationship between plane measurement results, drawing sequence numbers and 3D measurement objects;

[0018] The optical critical dimension of the 3D measurement object is calculated according to the plane measurement result, the image acquisition sequence number and the 3D model relationship of the 3D measurement object.

[0019] Furthermore, the acquisition of plane measurement results of the 3D measurement object by the microscope at different heights, each plane measurement result corresponding to a map acquisition sequence number, includes the following steps:

[0020] The wafer is placed on the motion platform, and the microscope focuses on the measurement point. Starting from the focus position, the microscope is moved vertically up or down along the Z axis to a or b height as the preparation position.

[0021] The microscope moves along the Z axis from position a\b to position b\a, and image acquisition and plane calculation are started at the same time;

[0022] After reaching the designated position, the microscope stops moving and image acquisition and calculation are turned off.

[0023] Furthermore, the acquisition of plane measurement results of the 3D measurement object by the microscope at different heights, each plane measurement result corresponding to a map acquisition sequence number, includes the following steps:

[0024] (1) The microscope performs initial focusing, with the focus position O as the starting position;

[0025] (2) The microscope moves up or down along the Z axis by a preset distance to the a or b preparation position;

[0026] (3) The microscope moves downward or upward along the Z axis to b or a;

[0027] (4) When moving from a to b, switch to G color light, and take pictures and calculate the key dimensions of the plane every time you move a step;

[0028] (5) When b moves to a, switch to color light B, and take pictures and calculate the key dimensions of the plane every time it moves a step;

[0029] (6) Store the results into an array by number and save the image.

[0030] Furthermore, the 3D model relationship is as follows:

[0031] The microscope moves from a\b to b\a along the Z axis. Under G color light, the plane measurement results experience a process of divergence, convergence, and divergence. In the convergence stage, the data is stable and slowly increases or decreases.

[0032] The microscope moves from a\b to b\a along the Z axis. Under the B color light, the plane measurement results experience a process of divergence, convergence, and divergence. In the convergence stage, the data is stable and slowly decreases or increases.

[0033] The microscope moves from a\b to b\a along the Z axis. Under the mixing of G\B color light data, the plane measurement results experience a process of divergence, convergence, and divergence. In the convergence stage, the data is stable and almost unchanged.

[0034] Under the G\B color light data mixture, the most stable data is obtained in the convergence stage, the G\B color light mixed data is fused, the stability of the mixed data segment is evaluated, and the most stable stage data is extracted as the measurement result.

[0035] Further, the calculating the optical critical dimension of the 3D measurement object according to the plane measurement result, the image acquisition sequence number and the 3D model relationship of the 3D measurement object includes:

[0036] G\B color light data fusion;

[0037] Evaluate the stability of fused data;

[0038] Calculate the most stable data segment and output the results.

[0039] Furthermore, the G\B color light data fusion includes:

[0040] The data of G and B color light are fused by corresponding image acquisition numbers to obtain fused data of G\B color light.

[0041] Furthermore, the evaluating the stability of the fused data includes:

[0042] The standard deviation is used to evaluate the stability and the mean of the fused data is solved. More than three consecutive measurement data are used for calculation to obtain the stability evaluation and mean data of the fused data.

[0043] Furthermore, the calculation of the most stable data segment and the result output includes:

[0044] The one with the smallest standard deviation is regarded as the most stable one. According to the stability evaluation of the fused data and the mean data, the minimum stability evaluation parameter is obtained, and the image number corresponding to the minimum stability evaluation parameter is recorded.

[0045] Using the mean data as the final measurement output result;

[0046] Output the picture corresponding to the picture number.

[0047] The advantages of the present invention are that the present invention can use 3D technology to simply, cost-effectively and efficiently solve the problem of unstable and unreliable measurement results faced by existing 2D measurement methods in 3D measurement environments, and can accurately and stably measure the OCD of 3D models. Through a large amount of data verification, the method has good stability and accuracy, and has a high degree of matching with CDSEM. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0049] Figure 1 A schematic diagram of a visual model according to an embodiment of the present invention is shown.

[0050] Figure 2 A schematic diagram of a map collection process according to an embodiment of the present invention is shown.

[0051] Figure 3 A schematic diagram showing the relationship between the plane measurement results under G color light, the image acquisition sequence number, and the 3D measurement object.

[0052] Figure 4 A schematic diagram showing the relationship between the plane measurement results under B color light, the image acquisition sequence number, and the 3D measurement object.

[0053] Figure 5 A schematic diagram showing the relationship between the plane measurement results under GB color light mixing, the image acquisition sequence number, and the 3D measurement object. DETAILED DESCRIPTION

[0054] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0055] When facing products with high height, multiple layers or thick coating, the focusing stability of the microscope laser cannot be guaranteed. Moreover, the size varies greatly at different heights, so it is impossible to stabilize and distinguish the accuracy of the results. Therefore, this method proposes an OCD measurement method based on 3D model relationship to solve this problem.

[0056] Specifically, the present invention provides an OCD measurement method based on a 3D model relationship, comprising:

[0057] Collect the plane measurement results of the 3D measurement object when the microscope is at different heights, and each plane measurement result corresponds to a map acquisition sequence number;

[0058] Establish the 3D model relationship between plane measurement results, drawing sequence numbers and 3D measurement objects;

[0059] The optical critical dimension of the 3D measurement object is calculated according to the plane measurement result, the image acquisition sequence number and the 3D model relationship of the 3D measurement object.

[0060] Figure 1 A schematic diagram of a visual model according to an embodiment of the present invention is shown. Figure 2 A schematic diagram of a map collection process according to an embodiment of the present invention is shown.

[0061] like Figure 1 , 2 As shown in the figure, this method allows the microscope to move along the Z axis and uses the microscope to take pictures. As the height changes, the measured object also presents different performances, accompanied by changes in the key dimensions of the plane. This method takes the Z-axis focus position O as the center and moves in the range of offset = ±|ab| / 2. By collecting images of green (G) and blue (B) light at different heights, the data of the two colors are calculated respectively, and the two sets of data are fused. The test data shows that the stability of the plane measurement results and the change of the data have the following 3D model relationship:

[0062] (1) Figure 3 As shown, the microscope moves from a\b to b\a along the Z axis. Under G color light, the plane measurement results experience a process of divergence, convergence, and divergence. In the convergence stage, the data is stable and slowly increases or decreases.

[0063] (2) Figure 4 As shown, the microscope moves from a\b to b\a along the Z axis. Under the B color light, the plane measurement results experience a process of divergence, convergence, and divergence. In the convergence stage, the data is stable and slowly decreases and increases.

[0064] (3) Figure 5 As shown, the microscope moves from a\b to b\a along the Z axis. Under the mixing of G\B color light data, the plane measurement results experience a process of divergence, convergence, and divergence. In the convergence stage, the data is stable and almost unchanged.

[0065] Through the analysis of the above data, it is concluded that when the G\B color light data is mixed, the most stable data is obtained in the convergence stage, and the result is close to the correct size. Therefore, this method fuses the G\B color light data, evaluates the stability of the mixed data segment, and extracts the most stable stage data as the measurement result. The specific method is as follows:

[0066] 1. G\B color light data collection

[0067] Wafer is located on the motion platform, the microscope performs initial focusing on the measurement point, starting from the focus position (or near) O position, the microscope moves up\down along the Z axis by offset to the a\b position, and prepares the position; the microscope moves along the Z axis from the a\b position to the b\a position, the distance between a and b is 2 times the offset, and the microscope image acquisition and plane calculation are turned on at the same time; after reaching the specified position, the microscope stops moving, and the microscope image acquisition and calculation process is turned off, and data acquisition is completed. Specific process:

[0068] (1) The microscope performs initial focusing, with the focus position O as the starting position;

[0069] (2) The microscope moves up or down along the Z axis by a preset distance to the a or b preparation position;

[0070] (3) The microscope moves downward or upward along the Z axis to b or a;

[0071] (4) When moving from a to b, switch to G color light, and take pictures and calculate the key dimensions of the plane every time you move a step;

[0072] (5) When b moves to a, switch to color light B, and take pictures and calculate the key dimensions of the plane every time it moves a step;

[0073] (6) Store the results into an array by number and save the image.

[0074] In the above data acquisition process, the initial focusing is performed to allow the microscope to cover a clear position when moving along the Z axis; the microscope moves between positions a and b along the Z axis, and the G\B color light switching, microscope image acquisition and plane calculation processes are started at the same time, and the synchronization meets high requirements, thereby improving system efficiency; the image acquisition interval and Z-axis position of this process do not have a linear relationship, so the images are numbered in the order of taking pictures, and the corresponding calculation results and pictures are recorded.

[0075] Plane key dimension measurement is the key dimension measurement of 2D images, which includes a variety of measurement methods, such as line width, overlay, circle diameter, etc. The 3D imaging processing method is based on this method.

[0076] In the above, two sets of key size arrays are obtained. The following is the data processing and calculation.

[0077] 2. Data Processing

[0078] The data is fused, stability evaluated, and mean calculated. The specific contents are as follows:

[0079] (1) G\B color light data fusion

[0080] The value of the object measured under G color light is represented by g_cd(n), the value of the object measured under B channel is represented by b_cd(n), and the value of the object measured after G\B color light fusion is represented by gb_cd(n); perform data fusion, the fusion formula is:

[0081] gb_cd(n)=(g_cd(n)+b_cd(n)) / 2

[0082]

[0083]

[0084] The data of G and B color light are merged by corresponding serial numbers, and the fusion data of G\B color light is obtained;

[0085] (2) Evaluating the stability of fused data

[0086] This method uses standard deviation to evaluate stability and solves the corresponding mean at the same time. It takes three or more consecutive measurement data for calculation. gb_avg(n) represents the mean of the fused data, and gb_avg(n) represents the standard deviation of the fused data. The calculation using three data is as follows:

[0087] gb_avg(n)=avg(gb_cd(n),gb_cd(n+1),gb_cd(n+2))

[0088] gb_cd(n)=Sigma(gb_cd(n),gb_cd(n+1),gb_cd(n+2))

[0089] Serial number B_CD GB_Average GB_Sigma 1 gb_cd(1) gb_avg(1) gb_sigma(1) 2 gb_cd(2) gb_avg(2) gb_sigma(2) … … … … n-2 gb_cd(n-2) gb_avg(n-2) gb_sigma(n-2) n-1 gb_cd(n-1) n gb_cd(n)

[0090] In the above table, GB_Average represents the mean of the fused data, and GB_Sigma represents the standard deviation of the fused data.

[0091] The above obtains the stability evaluation and mean data of the fused data.

[0092] (3) Calculate the most stable data segment and output the results

[0093] The one with the smallest standard deviation is the most stable. Using the above data, we can find the minimum stability evaluation parameter: MIN(g_sigma(1), g_sigma(2)…g_sigma(n-2)), and record the image number minNum_g corresponding to the minimum value.

[0094] In order to achieve better filtering effect and adaptability, the mean value is used as the final result. By querying the above data, the measurement output result is obtained: g_avg(minNum_g);

[0095] The output image is the serial number corresponding to the minNum_g-th image.

[0096] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. An OCD measurement method based on 3D model relationship, characterized in that: include: Collect the plane measurement results of the 3D measurement object when the microscope is at different heights, and each plane measurement result corresponds to a map acquisition sequence number; Establish the 3D model relationship between plane measurement results, drawing sequence numbers and 3D measurement objects; The optical critical dimension of the 3D measurement object is calculated according to the plane measurement result, the image acquisition sequence number and the 3D model relationship of the 3D measurement object.

2. The OCD measurement method based on 3D model relationship according to claim 1, characterized in that: The acquisition of plane measurement results of the 3D measurement object by the microscope at different heights, each plane measurement result corresponding to a map acquisition sequence number, includes the following steps: The wafer is placed on the motion platform, and the microscope focuses on the measurement point. Starting from the focus position, the microscope is moved vertically up or down along the Z axis to a or b height as the preparation position. The microscope moves along the Z axis from position a\b to position b\a, and image acquisition and plane calculation are started at the same time; After reaching the designated position, the microscope stops moving and image acquisition and calculation are turned off.

3. The OCD measurement method based on 3D model relationship according to claim 2, characterized in that: The acquisition of plane measurement results of the 3D measurement object by the microscope at different heights, each plane measurement result corresponding to a map acquisition sequence number, includes the following steps: (1) The microscope performs initial focusing, with the focus position O as the starting position; (2) The microscope moves up or down along the Z axis by a preset distance to the a or b preparation position; (3) The microscope moves downward / upward along the Z axis to b / a; (4) When moving from a to b, switch to G color light, and take pictures and calculate the key dimensions of the plane every time you move a step; (5) When b moves to a, switch to color light B. Each time it moves a step, it collects images and calculates the key dimensions of the plane. (6) Store the results into an array by number and save the image.

4. The OCD measurement method based on 3D model relationship according to any one of claims 1 to 3, characterized in that: The 3D model relationship is as follows: The microscope moves from a\b to b\a along the Z axis. Under G color light, the plane measurement results experience a process of divergence, convergence, and divergence. In the convergence stage, the data is stable and slowly increases or decreases. The microscope moves from a\b to b\a along the Z axis. Under the B color light, the plane measurement results experience a process of divergence, convergence, and divergence. In the convergence stage, the data is stable and slowly decreases or increases. The microscope moves from a\b to b\a along the Z axis. Under the mixing of G\B color light data, the plane measurement results experience a process of divergence, convergence, and divergence. In the convergence stage, the data is stable and almost unchanged. Under the G\B color light data mixture, the most stable data is obtained in the convergence stage, the G\B color light mixed data is fused, the stability of the mixed data segment is evaluated, and the most stable stage data is extracted as the measurement result.

5. The OCD measurement method based on 3D model relationship according to claim 4, characterized in that: The calculating the optical critical dimension of the 3D measurement object according to the plane measurement result, the image acquisition sequence number and the 3D model relationship of the 3D measurement object includes: G\B color light data fusion; Evaluate the stability of fused data; Calculate the most stable data segment and output the results.

6. The OCD measurement method based on 3D model relationship according to claim 5, characterized in that: The G\B color light data fusion includes: The data of G and B color light are fused by corresponding image acquisition numbers to obtain fused data of G\B color light.

7. The OCD measurement method based on 3D model relationship according to claim 6, characterized in that: The stability of the evaluated fusion data includes: The standard deviation is used to evaluate the stability and the mean of the fused data is solved. More than three consecutive measurement data are used for calculation to obtain the stability evaluation and mean data of the fused data.

8. The OCD measurement method based on 3D model relationship according to claim 7, characterized in that: The calculation of the most stable data segment and the result output include: The one with the smallest standard deviation is regarded as the most stable one. According to the stability evaluation of the fused data and the mean data, the minimum stability evaluation parameter is obtained, and the image number corresponding to the minimum stability evaluation parameter is recorded. Using the mean data as the final measurement output result; Output the picture corresponding to the picture number.

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