A method for obtaining spot information of incident light, measuring a focal plane and fitting a band of an optical metrology system

Abstract

The present invention relates to a method for obtaining spot information of incident light, measuring a focal plane, and fitting a band of an optical metrology system, including: obtaining a standard test sample, on which a measurement area including a characteristic graphic structure is provided, and the incident light is projected onto the standard test sample to form a spot; moving the standard test sample along at least one direction so that the spot scans the measurement area, and collecting the reflected light of the spot multiple times during the movement to obtain measurement values of multiple groups of measurement parameters related to the characteristic graphic structure; determining the size of the spot based on the size of the measurement area and a reliable test interval; obtaining the spot size and position through a unified standard test method and evaluation method, no longer relying on the subjective evaluation of the spot image, and the data is from the measurement results of the metrology system, which is objective and reliable; for broadband measurement, the measurement results can be from the test data of different bands, so the spot size of the target band can be effectively measured.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor measurement equipment, and particularly to a method for obtaining spot information, measuring focal plane and fitting band of incident light of an optical metrology system. Background Art

[0002] Semiconductor measurement equipment plays a crucial role in the yield control of semiconductor front-end and back-end processes. As the integration degree of semiconductor devices becomes higher and higher, the number of electronic devices per unit volume on the wafer increases, and the measured area size and critical parameter size are further reduced. In optical critical dimension measurement, the optical design and integrated assembly method of the probe jointly determine the size of the measurement spot, and the size of the measurement spot directly determines the minimum area size that can be measured. Therefore, an evaluation method is needed to measure the spot size and position of the measurement equipment probe, so as to provide guidance for optical design, assembly improvement and practical application, etc.

[0003] At present, the common method for evaluating the spot size and position is to directly obtain the spot pattern through a CCD camera alignment system to estimate the spot size and position. However, the subjective judgment of this method has too much influence: due to different material properties of different observation wafers, the spot patterns will be significantly different. Due to the lack of reference standards, it is difficult to formulate exposure parameter standards; even for the same observation wafer, due to factors such as the surface undulation and unevenness of the wafer, the spot patterns at different positions may also be different, and the customization and verification of the calibration wafer are also a major problem. In addition to the above factors, the spot pattern obtained through the CCD camera can only reflect the spot size and position information in the visible light band, and for a broadband measurement system, the spot information in the infrared and ultraviolet bands is unknown. Summary of the Invention

[0004] In view of the technical problems existing in the prior art, the present invention provides a method for obtaining spot information, measuring focal plane and fitting band of incident light of an optical metrology system. Aiming at the deficiencies in the subjective evaluation of the spot size and position of the measurement system through the alignment system at present, the spot size and position are obtained through a unified standard test method and evaluation method, and no longer rely on the subjective evaluation of the spot image. The data comes from the measurement results of the measurement system, which is objective and reliable; for broadband measurement, the measurement results can come from test data in different bands, so the spot size of the target band can be effectively measured.

[0005] According to the first aspect of the present invention, a method for obtaining spot information of incident light of an optical metrology system is provided, including:

[0006] Step 1, obtaining a standard test sample, wherein a measurement area including a characteristic graphic structure is arranged on the standard test sample, the incident light is projected onto the standard test sample to form a spot, and the size of the measurement area is larger than the size of the spot;

[0007] Step 2: Move the standard test sample along at least one direction so that the light spot scans the area to be measured, and collect the reflected light of the light spot multiple times during the movement to obtain multiple sets of measured values of measurement parameters related to the characteristic graphic structure. Among them, when collecting for the first time and the last time, at least a part of the light spot is located outside the area to be measured, and between the first collection and the last collection, there is at least one collection when the entire light spot is located inside the area to be measured;

[0008] Step 3: Determine the reliable test interval of the measurement parameter based on multiple sets of the measured values;

[0009] Step 4: Determine the size of the light spot based on the size of the area to be measured and the reliable test interval.

[0010] On the basis of the above technical solutions, the present invention can also be improved as follows.

[0011] Optionally, the characteristic graphic structure includes a grating structure;

[0012] The movement is multiple equal-step movements or continuous movement, and the time interval between each collection of the reflected light of the light spot is the same;

[0013] The multiple collections further include: before each collection, focus on the grating structure.

[0014] Optionally, the movement along at least one direction includes: moving along two mutually orthogonal directions respectively.

[0015] Optionally, the measurement parameter includes at least one of the topography parameter of the characteristic graphic structure, the light intensity of the reflected light, the polarization amplitude value ratio of the reflected light, and the phase ratio of the reflected light.

[0016] Optionally, step 3 further includes:

[0017] Determine the reliable test interval based on the credibility evaluation parameter of multiple sets of measured values of the topography parameter of the characteristic graphic structure. The credibility evaluation parameter includes the mean square deviation, the root mean square deviation of the measured values of the topography parameter of the characteristic graphic structure, or the goodness of fit of the measured values.

[0018] Optionally, the method for obtaining the light spot information of the incident light of the optical metrology system further includes:

[0019] Obtain a data evaluation reference value. Obtaining the data evaluation reference value includes obtaining the measured value or the value of the credibility evaluation parameter of the topographic parameter measurement value of the characteristic graphic structure when the light spot of the incident light is entirely located in the central region of the region to be measured. The central region is a region formed with the central position of the region to be measured as the center of the circle and a threshold length r as the radius.

[0020] Optionally, step 3 further includes:

[0021] Set a first threshold range based on the data evaluation reference value. The moving interval of the standard test specimen corresponding to the value of the measured value or the credibility evaluation parameter of the topographic parameter measurement value of the characteristic graphic structure within the first threshold range is the reliable test interval.

[0022] Optionally, step 3 further includes:

[0023] Obtain the value of the first derivative. Obtaining the value of the first derivative includes: setting a curve fluctuation threshold based on the data evaluation reference value, and removing multiple groups of the measured values or multiple groups of the values of the credibility evaluation parameters of the topographic parameter measurement values of the characteristic graphic structure outside the curve fluctuation threshold range; obtaining the first derivative curve of the remaining multiple groups of the measured value curves or the first derivative curve of the credibility evaluation parameter curves of the remaining multiple groups of the topographic parameter measurement values of the characteristic graphic structure; the value of the first derivative is the value of the first derivative curve of the remaining multiple groups of the measured value curves or the value of the first derivative curve of the credibility evaluation parameter curves of the remaining multiple groups of the topographic parameter measurement values of the characteristic graphic structure; set a second threshold range, and the moving interval of the standard test specimen corresponding to the value of the first derivative within the second threshold range is the reliable test interval.

[0024] Optionally, step 3 further includes:

[0025] Set a first threshold range based on the data evaluation reference value. The moving interval of the standard test specimen corresponding to the value of the measured value or the credibility evaluation parameter of the topographic parameter measurement value of the characteristic graphic structure within the first threshold range is the first reliable test interval;

[0026] Obtain the value of the first derivative. Obtaining the value of the first derivative includes obtaining the first derivative curve of multiple groups of the measured value curves or the first derivative curve of the credibility evaluation parameter curves of multiple groups of the topographic parameter measurement values of the characteristic graphic structure. The value of the first derivative is the value of the first derivative curve of multiple groups of the measured value curves or the value of the first derivative curve of the credibility evaluation parameter curves of multiple groups of the topographic parameter measurement values of the characteristic graphic structure. Set a second threshold range, and the moving interval of the standard test specimen corresponding to the value of the first derivative within the second threshold range is the second reliable test interval;

[0027] Use the overlapping interval of the first reliable test interval and the second reliable test interval as the reliable test interval.

[0028] Optionally, in step 4, the size of the light spot is the difference between the length of the area to be measured and the length of the reliable test interval in the moving direction of the standard test sample.

[0029] Step 4 further includes determining the position of the light spot based on the size of the area to be measured and the reliable test interval: taking the two mutually perpendicular and opposite moving directions of the standard test sample as the positive x-axis direction and the positive y-axis direction respectively, taking the center of the moving interval after the movement of the standard test sample as the origin, and taking the symmetric position of the center position of the reliable test interval with respect to the origin as the position of the light spot.

[0030] According to the second aspect of the present invention, there is provided a method for obtaining the measurement focal plane of an optical metrology system, including:

[0031] Step 1', obtain the vertical distance between the measurement head of the optical metrology system and the standard test sample, and the measurement head projects the incident light onto the standard test sample to form a light spot.

[0032] Step 2', adjust the vertical position of the measurement head and / or the standard test sample to obtain multiple different vertical distances, and use the method for obtaining the light spot information of the incident light of the optical metrology system described in the first aspect to determine the sizes of the light spots corresponding to different vertical distances.

[0033] Step 3', compare the sizes of the light spots corresponding to different vertical distances, obtain the light spot with the smallest size and the vertical distance corresponding to the light spot with the smallest size, and obtain the measurement focal plane from the vertical distance corresponding to the light spot with the smallest size, and the measurement focal plane is the plane for measuring the sample.

[0034] According to the third aspect of the present invention, there is provided a method for obtaining the fitting band of an optical metrology system, including:

[0035] Step 1'', obtain the band of the incident light projected onto the standard test sample, and the band of the incident light is a wide spectral band; obtain the signal light spectrum of the standard test sample based on the incident light in the wide spectral band.

[0036] Step 2'', perform fitting in multiple different bands based on the signal light spectrum, and the multiple different bands are a continuous band or all bands of the band of the incident light, or the multiple different bands are a discontinuous band composed of multiple continuous bands of the band of the incident light.

[0037] Step 3'', determine the sizes of the spots corresponding to different fitting bands by using the method for obtaining the spot information of the incident light of the optical metrology system described in the first aspect;

[0038] Step 4'', compare the sizes of the spots corresponding to the different fitting bands, and use the fitting band corresponding to the spot with the smallest size as the optimal fitting band.

[0039] The method for obtaining the spot information of the incident light of the optical metrology system, measuring the focal plane and the fitting band provided by the embodiment of the present invention scans and measures a to-be-measured area with a known size in different directions respectively. The spot goes from outside the to-be-measured area to inside the to-be-measured area and then to outside the to-be-measured area, and relevant measurement parameters are obtained. By data processing, a reliable test interval corresponding to the relevant measurement parameters is extracted, so as to obtain the spot size and position information of the measurement system; the spot size and position are obtained through a unified standard test method and evaluation method, and no longer rely on the subjective evaluation of the spot image. The data comes from the measurement results of the measurement system, which is objective and reliable; for broadband measurement, the measurement results can come from the test data of different bands, so the spot size and position of the target band can be effectively measured; it can assist in defining the optimal test focal plane and the optimal test band. Brief Description of the Drawings

[0040] Figure 1 It is a flowchart of an embodiment of the method for obtaining the spot information of the incident light of the optical metrology system provided by the present invention;

[0041] Figure 2 It is a schematic diagram of an embodiment of the microstructure within the to-be-measured Pad area provided by the present invention;

[0042] Figure 3 It is a schematic diagram of an embodiment of the relative X / Y direction movement of the to-be-measured area and the spot on the standard test sample provided by the present invention;

[0043] Figure 4(a) is a schematic diagram of an embodiment of the MSE result of the X-direction scanning measurement provided by the present invention;

[0044] Figure 4(b) is a schematic diagram of an embodiment of the MSE result of the Y-direction scanning measurement provided by the present invention;

[0045] Figure 5 It is a flowchart of an embodiment of the method for obtaining the measurement focal plane of the optical metrology system provided by the present invention;

[0046] Figure 6 It is a flowchart of an embodiment of the method for obtaining the fitting band of the optical metrology system provided by the present invention. Detailed Description of the Embodiments

[0047] The principles and features of the present invention will be described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0048] Figure 1 It is a flowchart of a method for obtaining the spot information of the incident light of an optical metrology system provided by the present invention. As Figure 1 shown, the method for obtaining the spot information of the incident light of the optical metrology system includes:

[0049] Step 1, obtain a standard test sample. A test area including a characteristic graphic structure is set on the standard test sample. The incident light is projected onto the standard test sample to form a spot, and the size of the test area is larger than the size of the spot.

[0050] Among them, different-sized test areas are distributed on one standard test piece for testing. In the embodiments provided by the present invention, the test area can be a PAD area, and the PAD area refers to a test area with a certain determined-size structure in a certain repeated Die on the wafer. The film layer structure in the test area is known or unknown, and it must be kept uniform, that is, the range of the structural parameters (such as film thickness) in the test area should be less than the static repeatability value of the measurement of the structural parameter. The static repeatability value can be the tolerance value measured multiple times when the position of the moving stage remains unchanged. The area outside the test area has a different film layer structure from the test area.

[0051] As Figure 2 shown is a schematic diagram of an embodiment of the microstructure in a test Pad area provided by the present invention. Figure 2 In the given embodiment, the size of the test Pad area selected on the standard test sample is 100μm×100μm. Figure 2 The upper right part in is a partial enlarged view of the test Pad area, and the microstructure / characteristic graphic structure in the test Pad area is a grating structure; the area on the standard test sample outside the test Pad area has a different structure (not shown in the figure).

[0052] The size of the test area of the standard test sample is larger than the size of the spot.

[0053] Step 2, move the standard test sample along at least one direction so that the spot scans the test area, and collect the reflected light of the spot multiple times during the movement to obtain multiple sets of measured values of measurement parameters related to the characteristic graphic structure. Among them, when the first collection and the last collection are performed, at least a part of the spot is located outside the test area, and between the first collection and the last collection, there is at least one collection when the spot is entirely located within the test area.

[0054] In specific implementation, the ultra-precision stage can drive the standard test sample to move multiple times with equal step distances. The moving ranges, step lengths, and directions of each movement of the standard test sample are defined in advance, and the corresponding motion position commands are sent to the controller of the ultra-precision stage. Each time the precision stage moves one step distance, spectral data is collected, and the receiving system receives the spectral reflection signal of the light spot.

[0055] Optionally, the ultra-precision stage can also drive the standard test sample to move continuously. Determine that the ultra-precision stage moves at a constant speed, and collect the reflected light of the light spot multiple times during the movement. The time intervals between each collection are the same, and thus the moving distance of the standard test sample corresponding to each collection can be obtained.

[0056] During the process of the ultra-precision stage driving the standard test sample to move, the light spot experiences three processes: all or at least part of the light spot is outside the Pad area to be measured, all of the light spot is within the Pad area, and all or at least part of the light spot is outside the Pad area to be measured again.

[0057] Step 3, determine the reliable test interval of the measurement parameter based on multiple groups of measurement values.

[0058] The reliable test interval refers to the interval segment where the measurement parameter is credible. The corresponding obvious feature is that at this time, the light spot completely falls within the area to be measured, and the information received by the data receiving end of the system completely comes from the information of the interaction between light and the internal structure of the area to be measured.

[0059] Step 4, determine the size of the light spot based on the size of the area to be measured and the reliable test interval.

[0060] The present invention provides a method for obtaining the spot information of the incident light of an optical metrology system. By scanning and measuring a to-be-measured area with a known Pad size in different directions, the light spot goes from outside the to-be-measured area to inside the to-be-measured area and then to outside the to-be-measured area, relevant measurement parameters are obtained. The reliable test interval corresponding to the relevant measurement parameters is extracted through data processing, so as to obtain the spot size and position information of the measurement system; the spot size and position are obtained through a unified standard test method and evaluation method, no longer relying on the subjective evaluation of the light spot image. The data comes from the measurement results of the measurement system, which is objective and reliable; for broadband measurement, the measurement results can come from the test data of different wavelength bands, so the spot size of the target wavelength band can be effectively measured; it can assist in defining the optimal test focal plane and the optimal test wavelength band.

[0061] Embodiment 1

[0062] Embodiment 1 provided by the present invention is an embodiment of a method for obtaining the spot information of the incident light of an optical metrology system provided by the present invention. Combining Figure 1 As can be seen, the embodiment of the method for evaluating the light spot includes:

[0063] Step 1: Obtain a standard test sample. There is a test area including a characteristic graphic structure on the standard test sample. Incident light is projected onto the standard test sample to form a light spot, and the size of the test area is larger than the size of the light spot.

[0064] In a possible embodiment, the test area can be a Pad area, and the characteristic graphic structure can be a grating structure. Figure 2 In the given embodiment, n1 and n2 respectively represent the refractive index values corresponding to two materials.

[0065] In the specific embodiment given by the present invention, as Figure 2 shown, a Pad area of 100um x 100um can be selected on the standard test sample, and within this Pad area, there is a grating structure with a period of 240nm and a duty cycle of 50%.

[0066] Step 2: Move the standard test sample in at least one direction so that the light spot scans the test area, and during the movement, collect the reflected light of the light spot multiple times to obtain multiple sets of measured values of measurement parameters related to the characteristic graphic structure. Among them, when collecting for the first time and the last time, at least a part of the light spot is outside the test area, and between the first collection and the last collection, there is at least one collection when the light spot is entirely within the test area.

[0067] In a possible embodiment, the movement is multiple equal-step movements or continuous movement, and the time interval between collecting the reflected light of the light spot each time is the same; among them, for multiple equal-step movements, collect the reflected light signal of the light spot after each movement, and also collect the reflected light signal of the light spot before the first movement; for continuous movement, it can move at a constant speed, and collect the reflected light signal of the light spot multiple times during the movement.

[0068] The multiple collections also include: Before each collection, focus on the grating structure. That is, after the standard test sample moves in any direction for any time, it also includes: Focus on the grating. Subsequently, the measurement system performs measurement, and the receiving system collects the measured values.

[0069] In specific implementation, digital grating autofocus can be achieved through the feedback of the laser rangefinder reading. The purpose of focusing is to lock the test area on the standard test sample within the tolerance range of the focal plane of the measurement system.

[0070] The movement of the standard test sample can be in any direction. In particular, in a possible embodiment, the any direction is the mutually orthogonal X direction and Y direction.

[0071] As Figure 3The figure shows a schematic diagram of the relative X / Y movement of the area to be measured on the standard test sample provided by the embodiment of the present invention with respect to the light spot. In actual situations, the position of the light spot remains unchanged, and the standard test sample is driven by a precision motion stage to move in equal steps or continuously.

[0072] In the specific embodiments given by the present invention, the central position of the area to be measured can be determined using the real-time images obtained by the alignment system, and this central position is defined as the central position for the measurement system to perform scanning measurement. The scanning range corresponding to the moving range of the standard test sample can be set to -100um to 100um relative to the central position, with a scanning step of 1um. A motion command is sent to the controller of the precision motion stage, and the ultra-precision motion stage drives the standard test sample to move along the X / Y directions with a step of 1um respectively.

[0073] In one possible embodiment, the measurement parameter is at least one of the critical dimension parameter of the film layer, MSE, GOF (Goodness of Fitting), the light intensity of the reflected light of the light spot, the ratio of the polarization amplitudes of the reflected light of the light spot, and the ratio of the phases of the reflected light of the light spot.

[0074] Specifically, the measurement parameter can be the critical dimension parameter of the film layer, such as the film thickness; it can also be a value reflecting the credibility of the critical dimension parameter, such as MSE or RMSE or GOF; it can also be the spectral test data received by the receiving system, such as the light intensity or the polarization light amplitude ratio, phase ratio, etc. obtained after processing.

[0075] Step 3, determine the reliable test interval of the measurement parameter based on multiple groups of measurement values.

[0076] In one possible embodiment, the reliable test interval is determined based on the credibility evaluation parameters of the measurement values of the morphological parameters of multiple groups of feature graphic structures. The credibility evaluation parameters include the mean square error, root mean square error of the measurement values of the morphological parameters of the feature graphic structures, or the goodness of fit of the measurement values.

[0077] In one possible embodiment, the method for obtaining the light spot information of the incident light of the optical metrology system further includes:

[0078] Obtain the data evaluation reference value. Obtaining the data evaluation reference value includes obtaining the measurement value or the value of the credibility evaluation parameter of the morphological parameter of the feature graphic structure when the entire light spot of the incident light is located in the central area of the area to be measured. The central area is an area formed with the central position of the area to be measured as the center of the circle and a threshold length r as the radius. Optionally, the threshold length r ≤ half of the length or width of the area to be measured. Taking Figure 2 the shown Pad area to be measured as an example, measurement is performed in the central area of this Pad area, and the MSE (Mean Square Error) is approximately 16, that is, the reference value is 16.

[0079] Specifically, the present invention provides three embodiments for determining a reliable test interval of a measurement parameter based on multiple sets of measurement values.

[0080] In the first possible embodiment, step 3 includes:

[0081] Setting a first threshold range based on a data evaluation reference value, and the moving interval of the standard test specimen corresponding to the value of the credibility evaluation parameter of the measurement value or the topographic parameter measurement value of the feature graphic structure within the first threshold range is the reliable test interval.

[0082] In the second possible embodiment, obtaining the value of the first derivative includes: setting a curve fluctuation threshold based on a data evaluation reference value, and eliminating the values of the credibility evaluation parameters of multiple sets of measurement values or multiple sets of topographic parameter measurement values of the feature graphic structure outside the curve fluctuation threshold range; obtaining the first derivative curve of the remaining multiple sets of measurement value curves or the first derivative curve of the credibility evaluation parameter curves of the remaining multiple sets of topographic parameter measurement values of the feature graphic structure; the value of the first derivative is the value of the first derivative curve of the remaining multiple sets of measurement value curves or the value of the first derivative curve of the credibility evaluation parameter curves of the remaining multiple sets of topographic parameter measurement values of the feature graphic structure; setting a second threshold range, and the moving interval of the standard test specimen corresponding to the value of the first derivative within the second threshold range is the reliable test interval. Wherein, the second threshold is a value close to zero. For example, the second threshold can be set to ±0.01, and the moving interval of the standard test specimen corresponding to the value of the first derivative ∈[-0.01, 0.01] is the reliable test interval.

[0083] In the third possible embodiment, setting a first threshold range based on a data evaluation reference value, and the moving interval of the standard test specimen corresponding to the value of the credibility evaluation parameter of the measurement value or the topographic parameter measurement value of the feature graphic structure within the first threshold range is the first reliable test interval;

[0084] Obtaining the value of the first derivative, obtaining the value of the first derivative includes obtaining the first derivative curve of multiple sets of measurement value curves or the first derivative curve of the credibility evaluation parameter curves of multiple sets of topographic parameter measurement values of the feature graphic structure, the value of the first derivative is the value of the first derivative curve of multiple sets of measurement value curves or the value of the first derivative curve of the credibility evaluation parameter curves of multiple sets of topographic parameter measurement values of the feature graphic structure, setting a second threshold range, and the moving interval of the standard test specimen corresponding to the value of the first derivative within the second threshold range is the second reliable test interval;

[0085] Taking the overlapping interval of the first reliable test interval and the second reliable test interval as the reliable test interval.

[0086] Extract a reliable test interval that meets the requirements from the first derivative curve of the reflection spectrum signal: In the reflection spectrum signal, the parameter values are close to the reference value (fluctuating within a certain range, and the fluctuation range varies according to different parameters), and the first derivative values are in the range of ± threshold δ (the value of threshold δ varies according to different parameters).

[0087] Step 4: Determine the size of the light spot based on the size of the area to be measured and the reliable test interval.

[0088] In a possible embodiment, in Step 4, the size of the light spot is the difference between the length of the area to be measured and the reliable test interval in the moving direction of the standard test sample.

[0089] In specific implementation, for equal-step movement, the number of movements can be determined according to the movement time and period of the standard test sample during reliable testing. Finally, the length of the reliable test interval in the moving direction of the standard test sample is the number of movements * the movement step of the standard test sample. The number of movements is the number of measurement points included in the reliable test interval (the number of times of collecting the reflected light of the light spot) minus 1. Correspondingly, for continuous movement, according to the moving speed of the standard test sample and the time interval for collecting the reflected light of the light spot, the length of the reliable test interval in the moving direction of the standard test sample is (the number of measurement points included in the reliable test interval - 1) * time interval * moving speed.

[0090] In a possible embodiment, Step 4 further includes determining the position of the light spot based on the size of the area to be measured and the reliable test interval: Taking the two mutually orthogonal and opposite moving directions of the standard test sample as the positive x-axis direction and the positive y-axis direction respectively, taking the center of the moving interval after the standard test sample moves as the origin, and the symmetric position of the center position of the reliable test interval about the origin is the position of the light spot.

[0091] In a specific embodiment provided by the present invention, select the value that reflects the measurement credibility of the key dimension parameter: MSE, and define the MSE growth threshold as 10%. As shown in Figures 4(a) and 4(b), they are schematic diagrams of the embodiments of the MSE results of the X-direction and Y-direction scanning measurements provided by the present invention respectively. In Figure 4(a), the abscissa X is the measurement point, 0 represents the center point of the X-direction scanning measurement, and the scanning range is the position -100μm to 100μm relative to the center point. In Figure 4(b), the abscissa Y is the measurement point, 0 represents the center point of the Y-direction scanning measurement, and the scanning range is the position -100μm to 100μm relative to the center point. If the reliable test interval includes m measurement points, then it corresponds to m spectral data, and the moving stage moves m - 1 step distances.

[0092] Through data processing, a reliable test interval that meets the requirements (MSE < 17.6) is extracted, as shown in Figure 4 (a) and Figure 4 (b), from which the size and position information of the light spot in the corresponding scanning direction can be obtained:

[0093] Spot size = length of the test area in the moving direction of the standard test sample - length of the reliable test interval in the moving direction of the standard test sample.

[0094] Spot position = - center position of reliable test interval, take '-' for Figure 3 The scanning direction is shown in the figure, and X is defined as rightward and Y is defined as upward. This value can reflect the distance and direction of the actual position of the light spot relative to the center point of the scanning measurement.

[0095] The size of the light spot in the X direction is 53um, and the center is 2um, which means that the actual position of the light spot in the X direction is 2um to the right of the scanning center point; the size of the light spot in the Y direction is 24um, and the center is -7um, which means that the actual position of the light spot in the Y direction is 7um downward from the scanning center point.

[0096] Example 2

[0097] Embodiment 2 provided by the present invention is an embodiment of a method for obtaining a focal plane measurement of an optical metrology system provided by the present invention. The optimal test focal plane of the measurement system is defined as the vertical test plane with the smallest spot size. However, the focal plane manually adjusted and controlled during the system adjustment process cannot effectively ensure the smallest spot size. Therefore, this method can be used to scan and measure different vertical test planes to find the vertical test plane with the smallest spot size, and update the optimal test focal plane of the measurement system online. Figure 5 A flowchart of an embodiment of a method for determining a measurement focal plane provided by an embodiment of the present invention, combined with Figure 5 It can be seen that the embodiment of the method for determining the measurement focal plane includes:

[0098] Step 1', obtaining the vertical distance between the measuring head of the optical metrology system and the standard test sample, the measuring head projects the incident light onto the standard test sample to form a light spot.

[0099] Step 2', adjusting the vertical position of the measuring head and / or the standard test sample to obtain a plurality of different vertical distances, and using a method for obtaining spot information of incident light of an optical metrology system provided by an embodiment of the present invention to determine the size of the spot corresponding to different vertical distances.

[0100] Step 3', compare the sizes of the spots corresponding to different vertical distances, obtain the smallest spot size and the vertical distance corresponding to the smallest spot size, and obtain the measurement focal plane from the vertical distance corresponding to the smallest spot size, which is the plane of the measurement sample.

[0101] In specific implementation, change the vertical distance between the probe of the measurement system and the standard test sample so that the standard test sample is on each vertical test surface, and repeat the method provided by the present invention for obtaining the spot information of the incident light of the optical metrology system to determine the size of the spot corresponding to different vertical distances, and obtain a reliable test range obtained after the standard test sample moves at equal step distances or continuously multiple times along any same horizontal direction on each vertical test surface, so as to determine the spot size and position corresponding to multiple vertical distances respectively. Among them, the vertical distance corresponding to the smallest spot size is the optimal measurement focal plane.

[0102] It can be understood that the method for obtaining the measurement focal plane of the optical metrology system provided by the present invention corresponds to the method for obtaining the spot information of the incident light of the optical metrology system provided by the foregoing embodiments. The relevant technical features of the method for obtaining the measurement focal plane of the optical metrology system can refer to the relevant technical features of the method for obtaining the spot information of the incident light of the optical metrology system, and will not be elaborated herein.

[0103] Embodiment 3

[0104] Embodiment 3 provided by the present invention is an embodiment of the method for obtaining the fitting band of the optical metrology system provided by the present invention. In ellipsometry (SE) measurement, the key dimension parameters of the material are obtained by comparing the measured spectral fitting value with the theoretical spectrum to find the closest theoretical spectrum and the corresponding theoretical dimension parameter value. Similarly, spectral reflectance (SR) measurement also uses a broadband light source to measure the reflectance of the structure to be measured, and finds the theoretical reflectance spectrum closest to the measured reflectance spectrum and the corresponding theoretical dimension parameter value as the result of the key dimension parameters of the material. Therefore, for the same measurement, different fitting bands will obtain different measurement results. For a film layer structure to be measured, the optimal fitting band can correspond to different optimization objectives according to different purposes and application methods. Here, the optimization objective can be defined as the smallest spot size of the corresponding fitting band so as to be able to measure as small a Pad structure as possible. As Figure 6 is a flowchart of an embodiment of the method for determining the fitting band provided by the embodiment of the present invention. Combining Figure 6 it can be seen that the embodiment of the method for determining the fitting band includes:

[0105] Step 1'', obtain the band of the incident light projected onto the standard test sample, and the band of the incident light is a broadband spectral band; obtain the signal light spectrum of the standard test sample based on the incident light of the broadband spectral band.

[0106] Step 2'', perform fitting for multiple different bands based on the signal light spectrum, and the multiple different bands are a continuous band or all bands of the band of the incident light, or the multiple different bands are a discontinuous band composed of multiple continuous bands in the band of the incident light.

[0107] Step 3'', using a method for obtaining spot information of incident light of an optical metrology system provided by an embodiment of the present invention, determine the sizes of spots corresponding to different fitting bands.

[0108] Step 4'', compare the sizes of spots corresponding to different fitting bands, and use the fitting band corresponding to the spot with the smallest size as the optimal fitting band.

[0109] In specific implementation, different measurement result parameter curves are obtained by changing the fitting band. The selection of the fitting band depends on the properties and structure of the film layer to be measured, and needs to include the characteristic (resonance) band of the material, corresponding to the characteristic peak on the spectrum. Subsequently, step 3'' is performed respectively, and the fitting band corresponding to the smallest spot size is defined as the optimal fitting band.

[0110] It can be understood that a method for obtaining the fitting band of an optical metrology system provided by the present invention corresponds to the method for obtaining the spot information of incident light of the optical metrology system provided by the foregoing embodiments. The relevant technical features of the method for obtaining the fitting band of the optical metrology system can refer to the relevant technical features of the method for obtaining the spot information of incident light of the optical metrology system, and will not be elaborated here.

[0111] A method for obtaining the spot information of incident light of an optical metrology system, measuring the focal plane and the fitting band provided by an embodiment of the present invention scans and measures a known-size area to be measured in different directions. The spot goes from outside the area to be measured to inside the area to be measured and then to outside the area to be measured, and relevant measurement parameters are obtained. By data processing, a reliable test interval corresponding to the relevant measurement parameters is extracted, so as to obtain the spot size and position information of the measurement system; the spot size and position are obtained through a unified standard test method and evaluation method, no longer relying on the subjective evaluation of the spot image, and the data comes from the measurement results of the measurement system, which is objective and reliable; for broadband measurement, the measurement results can come from test data of different bands, so the spot size and position of the target band can be effectively measured; it can assist in defining the optimal test focal plane and the optimal test band.

[0112] It should be noted that in the above embodiments, the descriptions of each embodiment have their own emphases. For the parts not detailedly described in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0113] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0114] The present invention will be described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processors of general-purpose computers, special-purpose computers, embedded computers, or other programmable data processing devices to generate a machine, such that the instructions executed by the processors of the computer or other programmable data processing devices generate means for implementing the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0115] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufacture including instruction means that implement the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0116] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0117] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concepts. Therefore, the appended claims are intended to be construed to include the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0118] Obviously, those skilled in the art can make various changes and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for obtaining spot information of incident light of an optical metrology system, characterized in that, Including: Step 1: Obtain a standard test specimen, on which a test area including a characteristic graphic structure is provided. Incident light is projected onto the standard test specimen to form a light spot, and the size of the test area is larger than the size of the light spot. Step 2: Move the standard test specimen in at least one direction so that the light spot scans the test area, and during the movement, collect the reflected light of the light spot multiple times to obtain multiple sets of measured values of measurement parameters related to the characteristic graphic structure. Among them, at the first collection and the last collection, at least a part of the light spot is outside the test area, and between the first collection and the last collection, there is at least one collection when the entire light spot is within the test area. Step 3: Determine a reliable test interval for the measurement parameters based on multiple sets of the measured values. Step 4: Determine the size of the light spot based on the size of the test area and the reliable test interval.

2. The method according to claim 1, wherein The characteristic graphic structure includes a grating structure. The movement is multiple equal-step movements or continuous movement, and the time interval between each collection of the reflected light of the light spot is the same. The multiple collections further include: before each collection, focus on the grating structure.

3. The method according to claim 1, characterized in that, The movement in at least one direction includes: moving in two mutually orthogonal directions respectively.

4. The method according to claim 1, wherein The measurement parameters include at least one of the topography parameters of the characteristic graphic structure, the light intensity of the reflected light, the polarization amplitude value ratio of the reflected light, and the phase ratio of the reflected light.

5. The method according to claim 4, characterized in that, Step 3 further includes: Determine the reliable test interval based on the credibility evaluation parameters of multiple sets of the measured values of the topography parameters of the characteristic graphic structure. The credibility evaluation parameters include the mean square deviation, the root mean square deviation of the measured values of the topography parameters of the characteristic graphic structure, or the goodness of fit of the measured values.

6. The method according to claim 1, characterized in that, The method for obtaining the light spot information of the incident light of the optical metrology system further includes: Obtain a data evaluation reference value. Obtaining the data evaluation reference value includes obtaining the measured value or the value of the credibility evaluation parameter of the measured value of the topography parameter of the characteristic graphic structure when the entire light spot of the incident light is located in the central area of the test area. The central area is an area formed with the center position of the test area as the center and a threshold length r as the radius.

7. The method according to claim 6, characterized in that, Step 3 further includes: Set a first threshold range based on the data evaluation reference value. The movement interval of the standard test specimen corresponding to the measured value or the value of the credibility evaluation parameter of the measured value of the topography parameter of the characteristic graphic structure within the first threshold range is the reliable test interval.

8. The method according to claim 6, characterized in that, Step 3 further includes: Obtaining the value of the first-order derivative, the obtaining of the value of the first-order derivative comprising: setting a curve fluctuation threshold based on the data evaluation reference value, and eliminating the values ​​of the credibility evaluation parameters of the multiple groups of measurement values ​​or the multiple groups of morphology parameter measurement values ​​of the characteristic graphic structures that are outside the curve fluctuation threshold range; obtaining the first-order derivative curves of the remaining multiple groups of measurement value curves or the first-order derivative curves of the credibility evaluation parameter curves of the remaining multiple groups of morphology parameter measurement values ​​of the characteristic graphic structures; the value of the first-order derivative is the value of the first-order derivative curve of the remaining multiple groups of measurement value curves or the value of the first-order derivative curve of the credibility evaluation parameter curve of the remaining multiple groups of morphology parameter measurement values ​​of the characteristic graphic structures; setting a second threshold range, and the movement interval of the standard test sample corresponding to the value of the first-order derivative within the second threshold range is the reliable test interval.

9. The method according to claim 6, wherein The step 3 also includes: A first threshold range is set based on the data evaluation reference value, and a moving interval of the standard test sample corresponding to a value of the credibility evaluation parameter of the measured value or the measured value of the morphological parameter of the characteristic graphic structure within the first threshold range is a first reliable test interval; Obtaining the value of the first-order derivative, wherein the first-order derivative value comprises obtaining the first-order derivative curves of the plurality of groups of measurement value curves or the first-order derivative curves of the credibility evaluation parameter curves of the plurality of groups of morphology parameter measurement values ​​of the characteristic graphic structures, wherein the first-order derivative value is the value of the first-order derivative curve of the plurality of groups of measurement value curves or the value of the first-order derivative curve of the credibility evaluation parameter curve of the plurality of groups of morphology parameter measurement values ​​of the characteristic graphic structures, and setting a second threshold range, wherein the movement interval of the standard test sample corresponding to the value of the first-order derivative within the second threshold range is a second reliable test interval; The overlapping section of the first reliable test section and the second reliable test section is used as a reliable test section.

10. The method according to claim 3, characterized in that In step 4, the size of the light spot is the difference between the length of the area to be tested and the length of the reliable test interval in the moving direction of the standard test sample; The step 4 also includes determining the position of the light spot based on the size of the area to be tested and the reliable test interval: the opposite directions of the two mutually orthogonal moving directions of the standard test sample are the positive direction of the x-axis and the positive direction of the y-axis respectively, the center of the moving interval after the standard test sample moves is taken as the origin, and the symmetrical position of the center position of the reliable test interval about the origin is the position of the light spot.

11. A method for obtaining the measurement focal plane of an optical metrology system, characterized in that, include: Step 1', obtaining a vertical distance between a measuring head of an optical metrology system and a standard test sample, wherein the measuring head projects the incident light onto the standard test sample to form a light spot; Step 2', adjusting the vertical position of the measuring head and / or the standard test sample to obtain a plurality of different vertical distances, and using the method for obtaining the spot information of the incident light of the optical metrology system according to any one of claims 1 to 10 to determine the size of the spot corresponding to the different vertical distances; Step 3', compare the sizes of the light spots corresponding to different vertical distances, obtain the light spot with the smallest size and the vertical distance corresponding to the light spot with the smallest size, and obtain the measurement focal plane from the vertical distance corresponding to the light spot with the smallest size. The measurement focal plane is the plane for measuring the sample.

12. A method for obtaining a fitting band of an optical metrology system, characterized in that, Including: Step 1'', obtain the wavelength band of the incident light projected onto the standard test piece. The wavelength band of the incident light is a broadband spectral band; obtain the signal light spectrum of the standard test piece based on the incident light in the broadband spectral band; Step 2'', perform fitting on multiple different wavelength bands based on the signal light spectrum. The multiple different wavelength bands are a continuous wavelength band or all wavelength bands of the wavelength band of the incident light, or the multiple different wavelength bands are a discontinuous wavelength band composed of multiple continuous wavelength bands in the wavelength band of the incident light; Step 3'', use the method for obtaining the spot information of the incident light of the optical metrology system according to any one of claims 1 to 10 to determine the sizes of the spots corresponding to different fitting wavelength bands; Step 4'', compare the sizes of the spots corresponding to different fitting wavelength bands, and use the fitting wavelength band corresponding to the spot with the smallest size as the best fitting wavelength band.

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